INHIBITORY EFFECT OF SELENIUM ON ENZYMES INVOLVED IN HEME BIOSYNTHETIC-PATHWAY IN CHICK-EMBRYOS

Effect of different concentrations of selenium (Se) on heme biosynthes is was studied at different developmental stages of chick embryo. The first rate limiting enzyme ALA-synthase (ALA-S; E.C. 2.3-1.37) activit y was enhanced by selenium, while hepatic and blood ALA-dehydratase ac tivity (ALA-d; E.C. 3.2.1.24) was decreased. Hepatic and blood free-su lfhydryl (SH) group contents were significantly decreased by Se. Furth er, hepatic aminolevulinic acid (ALA) and total blood porphyrin levels were enhanced and hepatic heme levels were depleted by selenium expos ure. Heme biosynthesis was maximally inhibited in the E4 (4th day inje cted embryos) when compared to later periods.