The effect of metal ions on the activity of delta-aminolevulinic acid dehydratase.

The effects of lead, iron, copper, and zinc ions on delta-aminolevulinic acid dehydratase from red blood cell haemolysates in humans, both in the absence and presence of plasma proteins, have been investigated. delta-aminolevulinic acid dehydratase (ALAD) was not found to be a specific indicator of blood lead concentrations since it was also inhibited by copper and activated by zinc. Plasma protein protected the enzyme from both inhibition and activation. ALAD activity was found to be an indicator of the total metal ion concentration in the blood and was therefore considered to be of doubtful value in screening large populations for increased lead absorption.     

The in vitro effect of zinc and other metal ions on the activity of human erythrocyte aminolaevulinic acid dehydratase.

Aminolaevulinic acid dehydratase (ALA-D) could be almost completely inhibited by EDTA when assayed in Tris—maleate and phosphate—citrate buffers. Inhibition was only partial in phosphate buffer and, in this case, the pH optimum of the enzyme shifted with increasing chelator concentration. Zinc activated the enzyme, though at high concentrations this effect was reversed. Zinc also reactivated enzyme after inhibition with EDTA. This reactivation was pH dependent and could elevate activity above the starting level. The role of zinc in the active enzyme is not one of maintaining its quaternary structure. Gel filtration showed a molecule of about 280,000 daltons both when the enzyme was active or inhibited with EDTA. The inhibitory effect of EDTA thus involves peripherally bound metal ions.     

The in vitro effect of zinc on the inhibition of human delta-aminolevulinic acid dehydratase by lead.

The antagonistic effect of zinc on inhibibition of human aminolevulinic acid dehydratase (ALAD) by lead was examined in vitro. The phenomenon was studied at pH 6.5-7.5 . Zinc and lead were added at concentrations ranging from physiological levels to levels far in excess of those expected in heavy industrial exposure. ALAD activity of normal blood assayed in the presence of zinc was unaffected by exogenous lead if the added zinc concentration was above 0.53 mmol/l blood, or double the normal endogenous level, and was of the order found in heavy industrial exposure to zinc. In this case, ALAD assay values were appreciably raised and might have fallen into the normal range in spite of a dangerous total blood lead of over 0.0048 mmol/l. When zinc was added in vitro to blood from a worker with a blood lead level of 0.0043 mmol/l the ALAD values obtained were also raised and did not reflect the dangerous level of lead in the patient.     

The in vitro effect of zinc on the inhibition of human delta-aminolevulinic acid dehydratase by lead.

The antagonistic effect of zinc on inhibibition of human aminolevulinic acid dehydratase (ALAD) by lead was examined in vitro. The phenomenon was studied at pH 6.5-7.5 . Zinc and lead were added at concentrations ranging from physiological levels to levels far in excess of those expected in heavy industrial exposure. ALAD activity of normal blood assayed in the presence of zinc was unaffected by exogenous lead if the added zinc concentration was above 0.53 mmol/l blood, or double the normal endogenous level, and was of the order found in heavy industrial exposure to zinc. In this case, ALAD assay values were appreciably raised and might have fallen into the normal range in spite of a dangerous total blood lead of over 0.0048 mmol/l. When zinc was added in vitro to blood from a worker with a blood lead level of 0.0043 mmol/l the ALAD values obtained were also raised and did not reflect the dangerous level of lead in the patient.     

In vitro study on lead and alcohol interaction and the inhibition of erythrocyte delta-aminolevulinic acid dehydratase in man

The effect of lead (Pb) and ethanol (EtOH) interaction on the inhibition of erythrocyte delta-aminolevulinic acid dehydratase (ALAD) was investigated in human blood in vitro. Two different doses of ethanol (equivalent to 16.28 mmol of EtOH/l of blood and 108.53 mmol of EtOH/l of blood) and lead (equivalent to 2.17 mumol of Pb/l of blood and 4.34 mumol of Pb/l of blood) were examined separately and in combination. The dose-effect (EtOH-ALAD) relationship for a wide range of ethanol concentrations (0-217.06 mmol of EtOH/l of blood) was also investigated. The results obtained indicate that ethanol by itself does not inhibit ALAD, while lead does it readily. Neither ethanol concentrations significantly altered ALAD activity. The dose-effect (EtOH-ALAD) relationship did not reveal any inhibitory effect of ethanol on ALAD either; however, a weak trend towards increased ALAD activity was found. The effect of ethanol combined with lead indicated no significant difference as compared to the effect of the same dose of lead per se; however, a weak trend towards decreased ALAD activity was found. These findings support the hypothesis that the effect of ethanol on the transient inhibition of ALAD activity in vivo does not occur directly, but possibly through the intermediary action of lead from the body lead pool.     

Blood lead and erythrocyte delta-aminolevulinic acid dehydratase levels in Manchester taxi drivers.

Among 40 Manchester taxi drivers the mean blood lead was 1.10 mumol/1 (22.8 mug per 100 ml). The mean erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity among 34 of them was 30.1 units. No significant association was found between the blood lead levels and erythrocyte ALAD activity in these 34 men. No significant association was found between either blood lead elvels or erythrocyte ALAD activity and duration of service or weekly mileage as a taxi driver or with drinking or smoking habits, or age. The mean blood lead of those with homes in the north east quadrant of the city was higher than of those living elsewhere but the difference was not statistically significant. Although there was no correlation between blood lead levels and the source of domestic water, the mean blood lead of those with lead domestic plumbing was appreciably higher than the level of those with copper plumbing. There was no indication that, by virtue of their occupation, the taxi drivers were liable to greater lead absorption than their fellow-citizens.     

Blood lead and erythrocyte delta-aminolevulinic acid dehydratase levels in Manchester taxi drivers.

Among 40 Manchester taxi drivers the mean blood lead was 1.10 mumol/1 (22.8 mug per 100 ml). The mean erythrocyte delta-aminolevulinic acid dehydratase (ALAD) activity among 34 of them was 30.1 units. No significant association was found between the blood lead levels and erythrocyte ALAD activity in these 34 men. No significant association was found between either blood lead elvels or erythrocyte ALAD activity and duration of service or weekly mileage as a taxi driver or with drinking or smoking habits, or age. The mean blood lead of those with homes in the north east quadrant of the city was higher than of those living elsewhere but the difference was not statistically significant. Although there was no correlation between blood lead levels and the source of domestic water, the mean blood lead of those with lead domestic plumbing was appreciably higher than the level of those with copper plumbing. There was no indication that, by virtue of their occupation, the taxi drivers were liable to greater lead absorption than their fellow-citizens.     

The effect of zinc and pH on the behaviour of delta-aminolevulinic acid dehydratase activity in baboons exposed to lead.

Four adult male baboons (Papio ursinus) were exposed to a cloud of lead oxide dust to induce changes in the status of delta-aminolevulinic acid dehydratase (ALAD). Enzyme activity fell rapidly to a steady state as blood lead levels rose above normal. Exogenous zinc was shown to activate the enzyme, and the antagonistic effect of zinc on in vivo and in vitro lead inhibition was demonstrated for baboons. In baboons not exposed to lead dust, ALAD showed an activity optimum at pH 7-1 which shifted to pH 6-8 with in vitro addition of lead. In baboons exposed to lead dust, with raised blood lead, activity optima were observed at pH 6-8 and 6-2, while the optimum at pH 7-1 was absent.     

The effect of zinc and pH on the behaviour of delta-aminolevulinic acid dehydratase activity in baboons exposed to lead.

Four adult male baboons (Papio ursinus) were exposed to a cloud of lead oxide dust to induce changes in the status of delta-aminolevulinic acid dehydratase (ALAD). Enzyme activity fell rapidly to a steady state as blood lead levels rose above normal. Exogenous zinc was shown to activate the enzyme, and the antagonistic effect of zinc on in vivo and in vitro lead inhibition was demonstrated for baboons. In baboons not exposed to lead dust, ALAD showed an activity optimum at pH 7-1 which shifted to pH 6-8 with in vitro addition of lead. In baboons exposed to lead dust, with raised blood lead, activity optima were observed at pH 6-8 and 6-2, while the optimum at pH 7-1 was absent.     

In vivo study on lead and alcohol interaction and the inhibition of erythrocyte delta-aminolevulinic acid dehydratase in man

The effect on alcohol (EtOH) consumption on the inhibition of erythrocyte delta-amino-levulinic acid dehydratase (ALAD) was investigated in 13 male lead workers and 7 "normal" male subjects. Lead and zinc protoporphyrin in blood and lead, delta-aminolevulinic acid, porphobilinogen and coproporphyrin in 24-h urine specimens were also determined. During 1 h the subjects drank 122.8 (SD 18.65) ml of an almost lead-free brandy, ie, a dose of 11.07 mmol/kg of body weight. This dose resulted in a trend toward a parallel decrease in ALAD activity and an increase in lead in blood (PbB), both of which approached the prealcohol value 24 h after the initial alcohol ingestion. A trend toward increased lead excretion in urine (PbU) was observed on the day of alcohol ingestion, as compared to the preceding and succeeding 24-h urine specimens. However, the observed increase in PbB and PbU cannot be attributed to the small amount of lead ingested through the brandy, ie, 7.09 (SD 1.06) nmol. The characteristic dose-effect relationship between PbB and ALAD (examined prior to and 1, 3, 5, and 24 h after the initial alcohol ingestion) reached the highest correlation coefficient 3 h after the initial alcohol ingestion (p less than 0.001). The data obtained appear to support the hypothesis of a possible role for the body lead pool and the lead-mediated influence of alcohol consumption on ALAD activity in man.     

Polymorphism of delta-aminolevulinic acid dehydratase and its effect on blood lead levels in Thai workers

To determine the prevalence of delta-aminolevulinic acid dehydratase (ALAD) polymorphism and its effects on blood lead levels (BLLs) in Thai workers, the authors performed a cross-sectional analysis of 389 Thai workers who were exposed to lead in a battery plant. The authors collected blood for BLLs and genotypic study, and they found that the allele frequencies of ALAD1 and ALAD2 were 0.98 and 0.02, respectively. They made a comparison of BLLs between genotype by dividing the levels into 2 categories of lead exposure (high and medium magnitude of exposure) and using length of employment as a covariance. Their results showed no significant difference of BLLs between the ALAD1-1 and ALAD1-2/ALAD2-2 groups in both levels of exposure. The frequency of ALAD2 in Thai workers was low; the authors found that ALAD polymorphism had a small or only modest effect on BLLs.     

Different behaviors of erythrocyte delta-aminolevulinic acid dehydratase. A comparison study between lead workers and normals.

Different characteristics of erythrocyte delta-aminolevulinic acid dehydratase (ALA-D1) between the workers with the history of occupational lead exposure and normals are described. In the blood of lead workers, when the hemolysates are heated at 60 C for five minutes, the activity of the erythrocytes ALA-D increases up to about 3.6-fold of an initial level, and as a result of heating the optimum in pH-activity curvee changes from pH 6.0 to pH 6.6, which is similar to the optimum pH of normal ALA-D. On the contrary, in normal blood, the optimum in the pH-activity curve is but little changed, even though the erythrocyte ALA-D activity is increased up to about 1.3-fold of the initial level by heating the hemolysates at 60 C for five minutes.     

Inhibition of liver, kidney, and erythrocyte delta-aminolevulinic acid dehydratase (porphobilinogen synthase) by gallium in the rat

Selective inhibition of enzymes in the heme biosynthesis pathway with concomitant urinary excretion of heme precursors serve as potentially important biological markers of chemical exposure and cell injury. Intratracheal administration of gallium arsenide particulate suspensions has been shown to result in inhibition of delta-aminolevulinic acid dehydratase (ALAD) in several tissues and increased excretion of the heme precursor aminolevulinic acid (ALA). This study was undertaken to evaluate in vivo the role of gallium alone in ALAD inhibition and increased urinary excretion of ALA. Male CD rats received a single ip injection of Ga2(SO4)3 at doses of 12.5, 25, 50, 100, and 200 mg Ga/kg. A dose-dependent inhibition of ALAD was observed 24 hr later in liver, kidney, and erythrocytes. After injection of 25 mg Ga/kg, maximal inhibition (42 to 49% of control) of ALAD occurred between 6 and 24 hr in liver and kidney with full recovery of activity at 96 hr. In erythrocytes, maximal inhibition (48% of control) occurred between 24 and 48 hr with recovery of activity at 96 hr. Mild to moderate renal proximal tubular necrosis in the pars recta was observed 24 hr after administration of 100 and 200 mg/kg, but no histopathologic changes were evident at lower doses. No consistent changes in urinary excretion of ALA were observed. Lineweaver-Burk analyses of renal and hepatic ALAD activities in the absence and presence of gallium indicated that the inhibition of ALAD by this element is noncompetitive (same Km, decreased Vmax). Gallium was shown to possess an inhibition constant (Ki) of approximately 3 microns for ALAD, similar to the Ki obtained for lead in other studies. Incubation of ALAD in vitro with gallium and lead, an active thiol group inhibitor, resulted in a greater inhibition of the enzyme. Further in vitro studies demonstrated the attenuation of gallium inhibition of hepatic and renal ALAD by zinc, suggesting that the mechanism of gallium action may involve competition for or displacement of zinc from the sulfhydryl group of the enzyme active site. Since ALAD inhibition occurred at doses at which no histopathologic changes were evident, the determination of ALAD activity in various tissues, including blood, may be of potential value as a biomarker of exposure/toxicity to metals such as gallium. The effect of chemical form and route of exposure of gallium and effects of other Group III metals on inhibition of ALAD and excretion of ALA is discussed.(ABSTRACT TRUNCATED AT 250 WORDS)