Δ-aminolevulinic Synthetase Activity Research Articles

Regulatory effect of copper on rat adrenal cytochrome P-450 and steroid metabolism

Accumulation of Cu 2+ in rat adrenal glands produced a biphasic response in concentrations of the mitochondrial cytochrome P-450 and heme which were, in turn, reflected in abnormal steroid biosynthesis and output. In the mitochondria, 1 day after Cu 2+ treatment, when the concentration of the metal ion was increased by 2- to 3-fold over the control value, a significant increase in cytochrome P-450-dependent steroid 11 β-hydroxylase activity was observed. These effects were accompanied by a nearly 85% increase in concentrations of cytochrome P-450 and heme. In addition, the activity of δ-aminolevulinate synthetase was increased by 3-fold. In those animals lipid peroxidation, assessed by measuring concentrations of conjugated dienes, was reduced to approximately 50% of the control value. However, after 7 days of Cu 2+ treatment (via a mini-osmotic pump), a significantly lowered rate of 11β-hydroxylase activity was noted, and the plasma concentration of corticosterone was also reduced significantly. Also, in the mitochondria, the concentrations of cytochrome P-450 and heme were decreased in comparison with the control values. These decreases were accompanied by elevated levels of the mitochondrial lipid peroxidation and a further increase in adrenal Cu 2+ content (5-fold). At this time, δ-aminolevulinate synthetase activity remained elevated but to a lower extent than that observed after 1 day of Cu 2+ treatment. In contrast to 11β-hydroxylase activity, the reduction in cytochrome P-450 content was not reflected in a decrease in the rate of cholesterol side-chain cleavage; rather this activity was increased in Cu 2+-treated animals. Adrenal heme oxygenase activity was unaffected by either Cu 2+ treatment, as was the specific content of cytochrome P-450 in the microsomal fraction. The present findings suggest that the Cu 2+-mediated regulation of cytochrome P-450-dependent steroidogenic activity in the adrenal mitochondria is predominately a reflection of the metal ion affecting heme biosynthesis and lipid peroxidation in this organ. Moreover, these actions appear to differentially affect the mitochondrial cytochrome P-450 species catalyzing different hydroxylation reactions in the adrenal steroidogenesis pathway.

Alterations of heme, cytochrome P-450, and steroid metabolism by mercury in rat adrenal

The treatment of male rats with Hg 2+ resulted in significant alterations in heme and hemoprotein metabolism in the adrenal gland which, in turn, were reflected in abnormal steroidogenic activities and steroid output. Twenty-four hours after the administration of 30 μmol of HgCl 2/kg (sc) the mitochondrial heme and cytochrome P-450 concentrations increased by approximately 50%. Also, Hg 2+ treatment stimulated a porphyrinogenic response which included an 11-fold increase in the activity of δ-aminolevulinate synthetase. The increase in mitochondrial cytochrome P-450 content was reflected in elevated steroid 11β-hydroxylase and cholesterol side-chain cleavage activities. In contrast, Hg 2+ treatment resulted in decreased concentrations of microsomal cytochrome P-450 (−75%) and heme (−45%). Similarly, the reduction in the microsomal cytochrome P-450 content was accompanied by reduced steroid 21α-hydroxylase and benzo[ a]pyrene hydroxylase activities. The mechanisms responsible for the loss of the microsomal cytochrome P-450 content appeared to involve a selective impairment of formation of the holocytochrome as well as an enhanced rate of heme degradation. This suggestion is made on the basis of findings that (a) the decrease in the microsomal cytochrome P-450 content was accompanied by a sevenfold increase in the activity of adrenal heme oxygenase, (b) no decrease in apocytochrome P-450 could be detected in sodium dodecyl sulfate-gel electrophoresis of the solubilized microsomal fractions stained for heme, and (c) the concentration of adrenal microsomal cytochrome b 5 was significantly increased in the Hg 2+-treated animals. It is suggested that Hg 2+ directly caused a defect in adrenal steroid biosynthesis by inhibiting the activity of 21α-hydroxylase. The apparent physiological consequences of this effect included lowered plasma levels of corticosterone and elevated concentrations of progesterone and dehydroepiandrosterone. This abnormal plasma steroid profile is indicative of a 21α-hydroxylase impairment.

Differential response of testicular and ovarian heme oxygenase activity to metal ions

The response of the microsomal heme oxygenase in the testis to metal ions distinctly differed from that of the ovarian source. The activity of the ovarian enzyme in rats treated with Co 2+ (250 μmol/kg, 24 h) responded in consonance with that of the liver and the kidney, i.e., heme oxygenase activity was elevated. In contrast, similar treatments did not increase the activity of testicular heme oxygenase. In addition, other metal ions, such as Cu 2+, Sn 2+, Pb 2+, and Hg 2+, known for their potency to increase heme oxygenase activity, were ineffective in increasing the enzyme activity in the testis. The unprecedented response of heme oxygenase in the testis to metal ions did not reflect an unusual nature of the enzyme protein insofar as it displayed a similar cofactor requirement and inhibition by known inhibitors of the enzyme activity, such as KCN and NaN 3. Moreover, the apparent K m 's for oxidation of hematoheme by the testicular and ovarian microsomal fractions were comparable and measured 2.3 and 1.4 μ m, respectively. In the testis of Co 2+-treated rats, the concentration of cytochrome P-450 in the rough and smooth endoplasmic reticular fractions was significantly decreased. The decrease in the hemoprotein level, however, did not reciprocate the activity of heme oxygenase in the fractions. The inability of metal ions to induce heme oxygenase activity in the testis did not represent the general refractory nature of the enzymes of heme metabolism to metal ions in this organ, since in rats treated with Co 2+ the activity of δ-aminolevulinate synthetase was significantly decreased 24 h after treatment. However, the activities of uroporphyrinogen-I synthetase, δ-aminolevulinate dehydratase, and ferrochelatase and the content of porphyrins were not altered in the testis of rats treated with Co 2+. The response of δ-aminolevulinate synthetase in the ovarian tissue to Co 2+ treatment contrasted that of the testis. In the ovary, the enzyme activity significantly decreased 6 h after treatment. This decrease was followed by a rebound increase at 24 h after administration of Co 2+. The presently described inability of metal ions to induce testicular heme oxygenase activity suggests that the activity of the enzyme in the testis is controlled by factor(s) which differ from those regulating the enzyme activity in other organs, including another steroidogenic organ, the ovary.

Enhancement and inhibition of enzymes of heme metabolism by diethyl maleate in the rat kidney

The effect of treatment of rats with the sulfhydryl agent, diethyl maleate, on heme metabolism in the kidney was investigated. Particular emphasis was placed on examining the effect of this agent on the activities of mitochondrial δ-aminolevulinate synthetase and microsomal heme oxygenase. The activity of δ-aminolevulinate synthease, the rate-limiting enzyme of heme biosynthesis, was increased in response to diethyl maleate treatment. The increase in enzyme activity was time and dose related, and could be inhibited by the administration of allylisopropylacetamide. Similarly, diethylmaleate treatment caused a time-dependent increase in the activity of heme oxygenase, the rate-limiting enzyme in heme degradation pathway. Diethyl maleate-mediated increase in the activities of heme oxygenase and δ-aminolevulinate synthetase could be inhibited by the administration of cycloheximide. Furthermore, stimulatory effects could not be elicited by in vitro treatment of the enzyme preparations with diethyl maleate. In addition, the activity of δ-aminolevulinate dehydratase was severely inhibited by diethyl maleate. However, the sulfhydryl agent was ineffective in altering the activities of uroporphyrinogen I synthetase, ferrochelatase, and biliverdin reductase. The increase in the activity of δ-aminolevulinate synthetase did not appear to be a feedback response to a decrease in cellular porphyrin and heme contents or a decrease in cellular glutathione level. It is suggested that diethyl maleate directly stimulates the synthesis of δ-aminolevulinate synthetase.

Studies on δ-Aminolevulinic Acid Synthetase Activity in Bone Marrow in Experimental Lead Poisoned Rats

Urinary increase of δ-aminolevulinic acid and coproporphyrin as well as basophilic stippled cells in the peripheral blood are the characteristic signs of lead poisoning. The biochemical lesion of porphyrin biosynthesis in lead poisoning is the partial inhibition of δ-aminolevulinic acid dehydratase, but whether or not δ-aminolevulinic acid synthetase is induced (stimulated) or not by lead is still unknown. This paper reports that δ-aminolevulinic synthetase activity in bone marrow in lead poisoned rats was 6.8 times higher than that of normal rats. Activity was found to increase within three or four days after lead administration and in parallel with the urinary increase of δ-aminolevulinic acid.The levels of urinary δ-aminolevulinic acid and coproporphyrin in lead poisoned rats decreased markedly following the administration of mitomycin c. This phenomenon were also observed in the case of hepatic porphyria caused by diethyl-1, 4-dihydro-2, 4, 6-trimethylpyridine-3, 5-dicarboxylate poisoned rats when treated with mitomycin c.These results strongly suggest that δ-aminolevulinic acid synthetase activity is induced either directly or indirectly by lead. Excessive δ-aminolevulinic acid thus formed seems to overcome the partial blocking of δ-aminolevulinic acid dehydratase resulting in the increased formation of coproporphyrin in lead poisoning.