Growth, digestibility and enzymatic activities in the pancreas and intestines of hamsters fed raw and heated soy flour

The nutritional effects of feeding raw and heated soy flour to young golden Syrian hamsters were investigated over a period of 32 days. Those animals fed raw soy flour grew much more poorly than those fed heated soy flour, an effect which was reflected in a lower food efficiency as well. Growth retardation of hamsters fed raw soy flour was accompanied by a lower apparent digestibility of the protein (54%) compared to heated soy flour (76%). The pancreases of animals fed raw soy flour were increased in size and had elevated levels of trypsin, chymotrypsin, amylase, and lipase. With the exception of trypsin activity in the small intestine, similar differences in enzyme activities between the raw and heated soy groups were generally found in the small intestine, cecum, large intestine, and feces. There was, however, a progressive decrease in these activities in the lower regions of the intestinal tract and feces. It is concluded that the hamster, in common with several other species of animals, is sensitive to the effects of the trypsin inhibitors in raw soy flour, and may provide a useful model for studying the long-term effects of trypsin inhibitors on the pancreas.     

Pancreatic response in rats and mice to trypsin inhibitors from soy and potato after short- and long-term dietary exposure

The effects on the pancreas of chronic (95 wk) dietary exposure to protease inhibitors from soy and potato were compared in rats and mice. Soy and potato trypsin inhibitor (TI) concentrates were prepared from defatted raw soy flour and potato juice, respectively, by selective precipitation and ultrafiltration. Animals were fed a diet in which casein supplied approximately 20% protein. Each concentrate (less than 1% of the diet) was added to provide 100 and 200 mg of trypsin inhibitor activity per 100 g of diet. In short-term (28 d) experiments in rats, both sources of TI decreased the apparent nutritional quality of casein and produced pancreatic hypertrophy consistent with a hormonally mediated feedback mechanism for pancreatic adaptation to diet that is interactive with the nutritional status of the animal. After long-term feeding (95 wk), soy and potato TI produced dose-related pancreatic pathology in rats consisting of nodular hyperplasia and acinar adenoma, which was typical of that associated with raw soy flour. Although mice responded similarly to rats to soy TI in short-term (28-d) feeding experiments, they were resistant to the formation of these lesions following long-term feeding. This considerable species variation in propensity to develop preneoplastic and neoplastic lesions of the pancreas is not predicted by the short-term hypertrophic and hyperplastic response of the pancreas to TI.     

Influence of several plant and animal proteins on rat pancreas

Twelve different plant and animal proteins were fed to rats for 4 weeks. Trypsin inhibitor (TI) content of the diet was significantly correlated with (although not directly related in all cases to) pancreas weights and with the pancreatic biochemical parameters that indicate hypertrophy. In vitro, but not in vivo, digestibility was correlated with the TI content of the diet. Quantity of DNA per gram pancreas was not found to be related to TI content. A second experiment compared graded levels of TI from raw or heated soy flour and soy protein isolate (SPI). The SPI diet produced higher relative pancreas weights per TIU than did the flour diets. Two commercial SPI's were fed as is or autoclaved in a third experiment. Autoclaving to very low TI values made no improvement in weight gain or pancreatic parameters measured, indicating that there may be a threshold level of TI below which rat pancreata do not respond, and that other factors in SPI are responsible for the slight pancreatic enlargement seen with SPI compared to casein.     

The failure of long-term feeding of raw soy flour, in the presence or absence of azaserine, to induce carcinogenic changes in the mouse pancreas

The effects of feeding mice raw or heated soy flours or casein in the presence and absence of injected azaserine were investigated over a period of 18 months. Although the feeding of raw soy flour (compared with heated soy flour or casein) caused a significant inhibition of growth and an enlargement of the pancreas, there was no macroscopic evidence of pancreatic nodules in any of the six experimental groups. Microscopic examination of the pancreas revealed a somewhat higher (not significant) incidence of atypical acinar cell nodules in all animals injected with azaserine, but this difference was little influenced by the diets themselves. We concluded that raw soy flour itself has no carcinogenic effect on the mouse pancreas and does not enhance the sensitivity of the mouse pancreas to azaserine. Thus, it cannot be assumed that the appearance of pancreatic nodules constitutes an obligatory sequela of pancreatic hypertrophy and/or hyperplasia in all species of animals.     

The failure of long‐term feeding of raw soy flour,in the presence or absence of Azaserine,to induce carcinogenic changes in the mouse pancreas

The effects of feeding mice raw or heated soy flours or casein in the presence and absence of injected azaserine were investigated over a peiod of 18 months. Although the feeding of raw soy flour (compared with heated soy flour or casein) caused a significant inhibition of growth and an enlargement of the pancreas, there was no macroscopic evidence of pancreatic nodules in any of the six experimental groups. Microscopic examination of the pancreas revealed a somewhat higher (not significant) incidence of atypical acinar cell nodules in all animals injected with azaserine, but this difference was little influenced by the diets themselves. We concluded that raw soy flour itself has no carcinogenic effect on the mouse pancreas and does not enhance the sensitivity of the mouse pancreas to azaserine. Thus, it cannot be assumed that the appearance of pancreatic nodules constitutes an obligatory sequela of pancreatic hypertrophy and/or hyperplasia in all species of animals.     

Protein digestibility and quality in products containing antinutritional factors are adversely affected by old age in rats

The protein digestibility-corrected amino acid score (PDCAAS) has been recommended to be the most suitable method for routine evaluation of protein quality of foods by FAO/WHO. The PDCAAS method includes the use of young rats for predicting protein digestibility of foods for all ages including the elderly. To assess the usefulness of protein digestibility in old rats in the calculation of PDCAAS for the elderly, the influence of age on the digestibility of protein in 5-wk-old and 20-mo-old rats by the balance method was studied. Fifteen protein products were tested. Each protein product was fed as the sole source of 10% dietary protein. A protein-free diet was also included to obtain an estimate of metabolic fecal protein. Protein digestibility values (corrected for metabolic fecal protein loss) in old rats were significantly (P < 0.05) lower than in young rats for most products; however, these differences were small (up to 3%) for properly processed animal products (casein, whey protein concentrate, whey protein hydrolysate, lactalbumin and skim milk powder). Similarly, the differences attributed to age were not large (up to 5%) for properly processed vegetable protein products (soy protein isolate and autoclaved soybean meal, black beans and fava beans). However, digestibility values in old rats were considerably lower (7-17%) than in young rats when fed products containing antinutritional factors, that is, mustard flour containing glucosinolates; alkaline/heat-treated soy protein isolate and lactalbumin-containing lysinoalanine; raw soybean meal and black beans containing trypsin inhibitors; and heated skim milk powder containing Maillard compounds. Therefore, the inclusion of protein digestibility data obtained using young rats in the calculations of PDCAAS may overestimate protein digestibility and quality of these products for the elderly. For products specifically intended for the elderly, protein digestibility should be determined using old rats.     

Rapid changes in pancreatic DNA, RNA and protein in the rat during pancreatic enlargement and involution

Pancreatic weight, nucleic acid content and protein content were measured on the involuting rat pancreas after its initial enlargement from a raw soy bean flour (RSF) diet. Rats were fed an RSF diet for four weeks and then changed to an inhibitor-free diet of either heated soy bean flour (HSF) or rat cubes for 1, 2, 7 or 14 days. Control rats were fed cubes continuously from weaning or cubes followed by HSF for two weeks. There was no significant difference in the body weights of rats in any of the test or control groups. After four weeks on RSF the wet weight of the pancreas was double that of the control animals and the protein content and nucleic acid content were also significantly greater. After RSF-fed animals were changed to cube or HSF diets, pancreatic parameters rapidly reverted to normal. The most striking change was in pancreatic DNA which returned to control values within 2 days of changing to cubes or HSF. Pancreatic weight, RNA and protein reverted to control values within 7 days of the change of diet. The rapid increase and decrease in the size of the rat pancreas after diet alterations suggest that pancreatic growth may be more labile than previously thought. If rapid changes in pancreatic cell number occur in rats fed alternating cube and RSF diets, then these animals may be more susceptible to pancreatic carcinogens.     

Effect of sulfur amino acid supplementation of raw soy flour on the growth and pancreatic weights of rats

Rat feeding studies showed that L-cystine, L-cysteine, N-acetyl-L-cysteine and L-methionine enhance the nutritional quality of raw (unheated) soy flour as measured in rats by the protein efficiency ratio (PER). Pancreas weights of rats fed diets supplemented with sulfur amino acids were higher than those of rats fed unsupplemented diets. In some instances this increase resulting from nutritional improvement of the diet was relatively greater than that in total body weight. Explanations are offered for these effects in terms of the proposed biofeedback mechanism involving the gastrointestinal endocrine system and the hormone cholecystokinin. The observed stimulation of pancreatic growth by added sulfur amino acids may be closely associated with this pancreatic regulatory mechanism when activated in response to dietary trypsin inhibitors present in unheated soy protein. The extent to which pancreatic hypertrophy develops as a result of a given exposure to trypsin inhibitors may be limited when the total amount or quality of the protein in the diet is less than optimal.     

The effects of long-term soy protein and milk protein feeding on the pancreas of Cebus albifrons monkeys

Twenty-seven 2- to 4-yr-old cebus monkeys (Cebus albifrons) were fed from infancy purified diets containing lactalbumin, soy isolate, casein or soy concentrate as the sole protein source. Hematologic and clinical chemistry values were similar for all groups. Head and tail portions of each pancreas were surgically removed for histopathologic evaluation and determination of protein, RNA and DNA content, and for trypsin and chymotrypsin activity. Hematoxylin and eosin-stained sections from 26 of 27 monkeys showed normal pancreatic tissue with occasional acinar vacuolation in all diet groups. The remaining animal, one of only two fed soy concentrate, had diffuse interstitial fibrosis of the pancreas associated with mild to moderate atrophy of acinar tissue. Biochemical analyses of the pancreatic biopsies indicated no group differences among animals fed lactalbumin, soy isolate or casein. One of two monkeys in the soy concentrate group showed decreased pancreatic protein, RNA and trypsin concentrations; this was probably due to the fibrosis in this animal. No evidence of pancreatic hypertrophy or hyperplasia, as measured by RNA/DNA and protein/DNA ratios, respectively, was seen in any diet group.     

Role of dietary protein in rat pancreatic enzyme secretory response to a meal

The role of dietary protein in the pancreatic enzyme secretory response to complete test meals was studied in rats fitted with chronic bile-pancreatic fistulas. Pancreatic enzyme secretory response was observed by collecting combined bile-pancreatic juice and continuously returning it to the intestine by a stream-splitter, which diverted 5% for assay. All rats were fed ad libitum a 24% casein diet during the recovery period. Four days postoperative, rats were infused intragastrically with 5 g of isonitrogenous, complete test meals containing casein (24%), alpha-protein (soy protein), amino acids patterned after casein or alpha-protein, casein + lima bean trypsin inhibitor (LBTI), and a nitrogen-free diet. Pancreatic enzyme secretion under basal conditions and in response to the test meals was determined. The pancreatic response to test meals containing intact casein as nitrogen source was the same as the response to nitrogen-free test meals, and was only slightly greater (not statistically significantly) than the response to test meals containing amino acids. Test meals containing alpha-protein, which was devoid of soybean trypsin inhibitor activity, were much more potent than corresponding amino acid test meals or nitrogen-free test meals. Addition of LBTI greatly increased the pancreatic response to casein test meals. The results indicate that intragastric infusion of diets containing casein as nitrogen source do not stimulate greater pancreatic enzyme secretion than test meals of nitrogen-free or amino acid diets under normal physiological conditions, and it is proposed that this is a consequence of the large reserve capacity of the exocrine pancreas.     

Effect of soy protein, casein and trypsin inhibitor on cholesterol, bile acids and pancreatic enzymes in mice

Dietary vegetable proteins may lower plasma cholesterol compared to animal proteins. We considered the possibility that lower digestibility and the trypsin inhibitor (TI) content of plant proteins could lead to alterations in bile acid metabolism and exocrine pancreatic function mediating some of this change. Mice were fed cholesterolemic diets of different protein source and TI content: casein, soy protein isolate, or casein plus TI for 4 weeks. Plasma and liver cholesterol were measured; pancreata, intestinal contents and mucosal scrapes were collected for bile acid, trypsin, chymotrypsin, amylase, and lipase assays. The soy group had lower plasma cholesterol levels. Intestinal bile acids in this group were higher, suggesting a causal relationship (increased bile acid secretion leading to increased cholesterol catabolism). Conversely, liver cholesterol in this group was raised, reflecting a possible shift in body cholesterol pools. TI addition did not affect lipid metabolism, though it did affect pancreatic function: it led to increased pancreatic weight and depressed intestinal trypsin activity, but elevated chymotrypsin and amylase levels in pancreas and intestine and increased trypsin levels in the pancreas. Therefore, soybean TI does not seem to affect cholesterol metabolism, though it greatly affects pancreatic secretion. On the other hand, soy protein has a marked effect on the bile acid and cholesterol metabolism, which may be a function of protein quality.     

The effect of fasting on enzyme levels in the enlarged and involuting rat pancreas

1. The effect on pancreatic digestive enzyme levels of fasting and changes from a diet containing trypsin inhibitor (raw soya-bean flour, RSF) to diets free of trypsin inhibitor (heated soya-bean flour, HSF, or commercial rat chow) was studied in rats for up to 7 d. 2. In RSF-fed rats killed without fasting, enzyme levels were low, but after fasting for 24 h before killing there was a marked increase in all enzyme levels. Histological studies showed that pancreatic acinar cells from RSF-fed rats killed without fasting were devoid of zymogen granules, but following a 24 h fast there was a marked accumulation of zymogen granules which extend into the basal cytoplasm. Fasting either produced no change or a fall in enzyme levels in rats fasted after feeding HSF or chow continuously. 3. If animals fed on RSF were changed to HSF and either fed or fasted for 24 h up to the time of killing there was an increase in amylase (EC 3.2.1.1), trypsin (EC 3.4.21.4), lipase (triacylglycerol lipase; EC 3.1.1.3) and protein 1 d after the change, followed by a fall over the next 6 d to levels similar to those seen in rats fed on HSF continuously. 4. Animals changed from RSF to chow showed similar effects as far as trypsin, lipase and protein were concerned, but amylase rose, to reach the level seen in rats fed on chow continuously (about ten times that seen in soya-bean-fed rats), after 2 d. 5. These results suggest that in the rats fed on RSF, pancreatic enzyme synthesis is rapid but secretion is equally rapid and intracellular enzyme levels are low. When these animals are fasted or changed to a diet free of trypsin inhibitor the rate of secretion falls but the high rate of synthesis continues for at least 24 h and enzymes accumulate in the pancreas. In studies of pancreatic enzyme levels in rats fed on trypsin inhibitor the extent of fasting before killing the animal is therefore an important variable. Such animals should probably not be fasted before study.     

Growth, digestibility, and enzyme activities in the pancreas and intestines of guinea-pigs fed on raw and heated soya-bean flour

The nutritional effects of giving raw (RSF) or heated (HSF) soya-bean flour to young guinea-pigs were investigated in trials 1 and 2, in which the levels of dietary protein were 120 and 190 g/kg diet respectively. The growth rate of animals fed on RSF was lower than that of those fed on HSF. Growth retardation of guinea-pigs fed on RSF was accompanied by a lower apparent digestibility of the protein (0.49-0.53) compared with HSF (0.67-0.76) and lower food conversion efficiency. In RSF-fed animals, increasing dietary protein affected growth and food conversion efficiency negatively. The pancreas of animals fed on RSF and HSF was similar in weight but secreted less trypsin, chymotrypsin and amylase, in RFS-fed animals. It was concluded that the mechanism by which raw soya-bean negatively affects the growth rate of guinea-pigs by reducing the activity of intestinal enzymes, differs from that suggested for rats and chicks, but is similar to that of pigs and calves.     

Nutritional effects of field bean (Vicia faba L.) proteinase inhibitors fed to rats.

1. Weanling rats were fed on purified-casein diets containing active and inactive (autoclaved) field bean (Vicia faba L.) proteinase inhibitors (PI) at levels of 1.25, 2.5, 5.0 and 10 g/kg. Diets containing raw- and autoclaved-field-bean meal (FBM) were also given. The body-weight gain, protein efficiency ratio (PER); i.e. the ratio of the live weight gain in g/g of protein consumed and apparent nitrogen digestibility were determined 7, 14 and 21 d after the start of the trial. 2. Significant growth depression (P less than 0.001) was observed in rats given diets containing 2.5 g/kg PI (27--35%). In rats fed on raw FBM growth depression was severe after 7 d (57%). 3. Food intake was depressed at PI inclusion levels of 5 g/kg and higher between 14 and 21 d. 4. PER was depressed significanlty (33-44%) in rats given diets containing the active PI at all levels after 7 d. The protein utilization of all casein diets was higher than that of the FBM diets. 5. Apparent N digestibility was depressed in rats fed on diets containing 10 g/kg PI by 9 and 7% at 14 and 21 d respectively. The N digestibility of both raw and heated FBM was similar at approximately 84%. 6. It was concluded that the PI are not the main factors responsible for the growth depression observed when raw FBM is fed to rats.     

Oligo-L-methionine and resistant protein promote cecal butyrate production in rats fed resistant starch and fructooligosaccharide.

We examined the role of resistant protein and peptides in promoting cecal butyrate production in rats fed rapidly fermentable carbohydrates. Rats were fed diets containing raw potato starch (RPS, 200 g/kg diet) or fructooligosaccharide (FOS, 60 g/kg diet) with casein, soy or rice protein (250 g/kg diet) for 13 d. In rats fed RPS with casein, the major cecal organic acid was acetate (441 micromol), but lactate and succinate were also found in considerable amounts (324 micromol). Succinate was the major cecal organic acid (235 micromol) in rats fed FOS with casein. When rice protein was fed with RPS, the contribution of lactate was significantly lower and that of propionate tended to be higher (P < 0.1) than in rats fed casein. In rats fed rice protein with FOS, cecal butyrate and acetate were greater and cecal succinate was lower than in rats fed casein with FOS (P < 0.05). Despite the similar amounts of undigested protein in rice and soy proteins, soy protein did not similarly affect cecal butyrate in rats fed FOS or RPS. In another experiment, rats were fed diets containing high amylose cornstarch (HAS, 200 g/kg diet) with casein, casein + oligo-L-methionine (OM, 3 g/kg diet), soy protein, soy protein + OM (3 g/kg diet) or rice protein (250 g/kg diet) for 10 d. OM (digestibility, 31%) was substituted for the same amount of casein. Rats fed rice protein had greater cecal butyrate than rats fed casein (P < 0.05). OM supplementation to casein or soy protein increased cecal butyrate compared with rats fed casein or soy protein alone (P < 0.05). These data support our hypothesis that resistant protein and peptides promote cecal butyrate production and suggest that the differing potency of rice and soy proteins in promoting cecal butyrate production might be explained in part by the different amino acid composition of resistant protein.     

Binding of navy bean (Phaseolus vulgaris) lectin to the intestinal cells of the rat and its effect on the absorption of glucose

The main objectives of this investigation were to study the binding of a lectin from navy beans with the epithelial cells of the rat intestine and to assess the effect of such binding on the ability of the intestine to absorb glucose. A Scatchard plot, based on the binding of 125I-labeled lectin to isolated intestinal epithelial cells, was used to calculate an association constant (Ka) of 15 x 10(6)M-1 and the number of binding sites per cell, 12 x 10(6). Metabolic studies were conducted over a period of 5 d on groups of rats fed raw or autoclaved navy bean flour and casein with or without the purified lectin. Growth, protein digestibility, biological value and net protein utilization were significantly lower in animals that had been fed raw navy bean flour or casein plus lectin than in control groups fed diets containing autoclaved navy bean flour or casein alone. Vascular perfusion was used to measure the rate of uptake of glucose by the intestines of rats that had received the various dietary treatments. The rate of absorption of [14C]glucose by intestines from rats fed raw navy bean flour or casein plus lectin was approximately one-half that of their counterparts fed the autoclaved flour or casein alone. These results provide evidence that the lectin, by virtue of its interference with intestinal absorption, is responsible, at least in part, for the nutritional inferiority of raw navy beans.     

Nutritional significance of a rice bran concentrate with trypsin inhibitor activity

A rice bran protein concentrate (RBPC) was prepared from de-fatted rice bran by extraction with a 1% sodium chloride solution and by acetone-precipitation. This protein concentrate contained 45% protein, which was as good as casein in terms of protein quality being judged from the results of amino acid analysis. On the other hand, RBPC possessed the trypsin inhibitor activity corresponding to the complete inhibition of about 6 mg of bovine trypsin per 1 g of dry material. The activity was, however, completely destroyed by autoclaving RBPC for 30 min at 121 degrees C. In vitro digestion tests showed that RBPC was easily digested by pepsin but was resistant to the attack by trypsin, compared with autoclaved RBPC. Concerning in vivo digestion, however, there was no significant difference in apparent nitrogen digestibility between RBPC and the heated RBPC. In growth experiments with weanling rats fed a 10% level of protein diet, growth depression and the tendency of slight pancreatic hypertrophy were observed in rats receiving a RBPC diet. It is presumed that one of the reasons which explains these phenomena is the presence of trypsin inhibitor in RBPC.     

Comparative inhibition of trypsins from several species by soybean trypsin inhibitors

Inhibition by soybean trypsin inhibitor (SBTI) preparations of trypsins and of total proteolytic activity from several species was compared. Rat, monkey, human, bovine, porcine and mink trypsins were all inhibited 90-100% by SBTI, although there were species differences at low SBTI concentrations. Extent of inhibition of trypsin from the various species did not correlate with SBTI-induced pancreatic enlargement. Total proteolytic activity was inhibited up to 40% in rat, monkey, and human preparations by SBTI, and inhibition curves were similar. SBTIs extracted from unheated soy protein isolate (USPI) or raw soy flour (RSF) were approximately equal in their ability to inhibit human trypsin. SBTI extracted from heated soy protein isolate (SPI) was slightly less effective in inhibiting human trypsin than SBTI from either RSF or USPI.     

Effects of dietary proteins and trypsin inhibitor on growth and lipid metabolism in hamsters

The purpose of this study was to determine trypsin inhibitor (TI) activity in sweetpotato and soy flour diets and their effects on the growth and lipid metabolism of hamsters. Male Golden Syrian hamsters were fed different types of dietary protein containing casein, soyprotein, transgenic sweetpotato plus soy flour (TSPF+SF), nontransgenic sweetpotato (NTSPF) plus soy flour (NTSPF+SF), transgenic sweetpotato (TSPF) and nontransgenic sweetpotato flour for 28 days. The TI activity was highest in TSPF+SF (19.30 TIU/mg) and NTSPF+SF (17.20 TIU/mg) diets that induced growth retardation in animals, lowest in TSPF (5.80 TIU/mg) and NTSPF (5.50 TIU/mg) diets, which did not affect the growth of the animals, and negligible in casein (<1.00 TIU/mg) and soyprotein (2.00 TIU/mg) diets. Plasma total cholesterol (TC), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C) and triglyceride (TG) concentrations were significantly higher in hamsters fed the casein diet compared to those fed the soy protein, TSPF+SF, NTSPF+SF, TSPF and NTSPF diets. A positive correlation was observed between plasma TC concentrations of hamsters and dietary methionine, lysine, leucine content and methionine/glycine ratios. Liver TC and TG concentrations of hamsters fed casein were significantly higher than those of all other diet groups. The supplementation of sweetpotato flour with soy flour increased both protein and TI activity in the diets and the lipid metabolism of hamsters were unaffected by TI activity.     

Consumption of soy protein isolate modulates the phosphorylation status of hepatic ATPase/ATP synthase beta protein and increases ATPase activity in rats

ATPase/ATP synthase plays important roles in the regulation of carbohydrate, protein, and lipid metabolism through modulating energy homeostasis. The purpose of this study was to examine the effects of feeding soy proteins and isoflavones (ISF) on the enzymatic activity and protein modification of hepatic mitochondrial ATPase/ATP synthase. In Expt. 1, Sprague-Dawley rats aged 50 d were fed diets containing either 20% casein or 20% alcohol-washed soy protein isolate (SPI) with or without supplemental ISF (770.7 micromol/kg diet) for 70 d. In Expt. 2, weanling Sprague-Dawley rats were fed diets containing 20% casein with or without added ISF (154.1 micromol/kg diet) or 20% SPI for 90 d. Hepatic mitochondrial ATPase activity was significantly higher in the rats fed SPI than in those fed casein. Addition of ISF to SPI eliminated the action of SPI. ATPase/ATP synthase beta protein contents in the liver were unchanged; however, its patterns measured by 2-dimensional Western blot were different among dietary groups. The rats fed SPI or SPI plus ISF had 3 more major protein spots with the same molecular weights (80 kDa and 55 kDa) as those presented in the rats fed casein but with different isoelectric points. Pretreatment of hepatic mitochondrial proteins from the rats fed casein with alkaline phosphatase produced the same ATPase/ATP synthase beta patterns as observed in the SPI-fed rats and significantly elevated the ATPase activity. These results suggest that consumption of soy proteins increases hepatic ATPase activity, which might be a consequence of increased dephosphorylation or decreased phosphorylation of the mitochondrial ATPase/ATP synthase beta protein.