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61.
Adenine aminohydrolase: occurrence and possible significance in trypanosomid flagellates. 总被引:3,自引:0,他引:3
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G W Kidder L L Nolan 《Proceedings of the National Academy of Sciences of the United States of America》1979,76(8):3670-3672
Adenine aminohydrolase (EC 3.5.4.2) from four species of Leishmania and from Crithidia fasciculata was examined for specific activities, affinity for substrate (adenine), and stability to heat. All were found to be strongly and non-competitively inhibited by both coformycin and deoxycoformycin, two tight-binding inhibitors of adenosine deaminase (adenosine aminohydrolase, EC 3.5.4.4). Deoxycoformycin is the more potent inhibitor of the two. Neither inhibitor was active against the purine phosphoribosyltransferases. When deoxycoformycin was added to the defined growth medium containing hypoxanthine as the purine source, the growth of C. fasciculata was unaffected, but when adenine was the purine source for the organism, severe inhibition resulted. This implies that hypoxanthine is the obligatory base for nucleotide synthesis and that the adenine phosphoribosyltransferase (AMP:pyrophosphate phosphoribosyltransferase, EC 2.4.2.7) is, in some manner,idenied access to exogenous substrate. 相似文献
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Choyke PL; Frank JA; Girton ME; Inscoe SW; Carvlin MJ; Black JL; Austin HA; Dwyer AJ 《Radiology》1989,170(3):713
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Jorge Jimenez MD Margarita Ochoa RN Maria Paz Soler RN Patricio Portales SW 《Contraception》1984,30(6):523-533
A long-term follow-up study compared development and health of 128 breast-fed children whose mothers had received depotmedroxyprogesterone acetate (depot-MPA) while lactating and 142 control children whose mothers had used mechanical contraceptives or no contraceptives or had undergone sterilization. The children, who were approximately 4-1/2 years old at follow-up, showed no ill effects on their growth and development and health status from exposure to depot-MPA. Depot-MPA-treated mothers lactated significantly longer than controls and also had greater parity than controls. These factors apparently contributed to a difference in weight at follow-up. Compared with the SempePedron standard, more of the depot-MPA group were underweight and more controls were overweight. 相似文献
67.
Magnetic resonance (MR) imaging, correlated with anatomic sections, was used to characterize the progressive and regressive changes in the nucleus pulposus in neonates. The spines of five fetuses and five full-term infants between 16 and 40 weeks old were studied. In anatomic sections, the nucleus pulposus was sharply demarcated from the anulus fibrosus, Sharpey fibers were conspicuous, and a plate of primitive notochord was evident in the equator of the disk. On long repetition time (TR)/long echo time (TE) or long TR/short TE MR images, Sharpey fibers (low signal intensity) and notochord (low signal intensity) could be differentiated from the high-signal-intensity nucleus pulposus and anulus fibrosus. The major differences between the fetal and infant spines were the amount of notochord in the disk and ossification in the vertebral body. 相似文献
68.
We have recently shown that 5% CO2/95% O2 in the serosal bathing solution, with 100% O2 in the mucosal solution, results in CO2-diffusion limitation of acid secretion in bullfrog gastric mucosa. Changing to 10% CO2/90% 02 on both surfaces doubles the acid secretory rate. We calculate that, were the rate of oxygen consumption to increase significantly as a result of secretory stimulation, the tissue would now be oxygen limited. This prediction is tested by raising the P02 by increasing the total pressure in a hyperbaric chamber. Since no change in acid secretory rate or potential difference was observed upon changing from PO2 = 0.9 to PO2 = 1.9 atm, we conclude that the tissue is not O2 limited at normal pressure. Decreasing PO2 below 0.9 atm, by contrast, decreases the acid secretory rate and raises both PD and resistance. We infer that the rate of oxygen consumption did not rise significantly when acid secretion was increased by supplying sufficient CO2. 相似文献
69.
G W Kidder 《The American journal of physiology》1983,245(2):G236-G241
Using hyperbaric conditions previously shown to give improved oxygen delivery to the chambered dogfish gastric mucosa, experiments were performed to further characterize this tissue under these conditions. Removal of Cl- depressed but did not abolish acid secretion, raised the transepithelial resistance, and caused the potential to become more negative with reference to the mucosal surface. Voltage clamping to -60 mV inhibited secretion significantly; voltage clamping to +60 mV sometimes gave a stimulation. There was no long time-constant transient response to current passage. Under hyperbaric conditions, addition of the normal 350 mM urea content of elasmobranch plasma stimulated secretion. A further increase in partial pressure of oxygen (PO2) above 1.9 atm had no effect on secretion. The current-voltage plot showed two breakpoints, one about -23 mV and a second (not always detectable) at +50 mV; the negative breakpoint was stable as PO2 changed from 0.9 to 1.9 atm. Many of these observations are different from those reported for normabaric tissue and closely resemble those in the isolated frog gastric mucosa. 相似文献
70.