Impact of Zinc toxic levels on Hepatic Heme Biosynthesis in Chick Embryos

Zinc as an essential trace element it is involved in various molecular and biological processes, and simultaneously toxic at high levels. Although, consequences of zinc deficiency have been recognised for many years, it is only recently that attention has been directed to the potential consequences of excessive zinc intake. All nucleated cells synthesize sufficient heme to meet the obligatory needs of mitochondrial cytochromes for cellular respiration, while certain tissues produce additional heme for their specialized roles. Biochemical studies of heme biosynthesis in experimental animals are useful to elucidate the mechanism underlying the different porphyria’s. Chick embryos were treated with 25 and 75m moles of Zinc / kg wt on 14th day of embryonic development. Embryos were sacrificed on 20th day for the collection of hepatic tissues. The levels of Aminolevulinic acid (ALA), heme and the activity of Aminolaevulinic acid synthase (ALA-S), Aminolaevulinic acid dehydratase (ALA- d) and heme synthetase were assayed in hepatic tissues of chick embryos. ALA-S activity was decreased in a dose dependent manner with zinc treatment. Whereas, ALA levels and ALA- d activity was unaltered and heme synthetase activity and hepatic heme levels were increased in a dose dependent manner with zinc treatment.