Selenium altered regulation of heme biosynthesis in chick embryos

A few selected indices of heme biosynthesis have been studied in liver and blood from chick embryos receiving different concentrations of selenium of toxicological significance 12.5, 25 and 37.5 mumoles/Kg egg.Wt.). The first rate limiting enzyme Aminolevulinic acid synthetase activity was enhanced by selenium treatment under both IN VIVO and IN VITRO conditions, while hepatic ALA dehydratase activity was unaltered. Hepatic and blood free sulfhydryl (-SH) group contents were significantly decreased by selenium. In accordance with these results, blood aminolevulinic acid dehydratase (ALA dehydratase) and hepatic ferrochelatase, both the sulfhydryl group requiring enzymes, were significantly inhibited. Further, hepatic ALA, total blood porphyrin levels were enhanced and hepatic heme levels were depleted by selenium exposure. These results suggest selenium as a novel regulator of heme biosynthesis by altering the activities of sulfhydryl group requiring enzymes of chick embryos.