A single form of metallothionein is present in both heavy metal induced and neonatal chicken liver

Abstract

Multiplicity of metallothionein and their genes in higher animals are documented extensively in recent literature. In contrast, chicken liver Produced apparently a single form of metallothionein upon heavy metal exposure. This protein was purified by gel filtration and ion exchange chromatography and another technique based on heat treatment and acetone fractionation, followed by ion exchange chromatography. In adult uninduced chicken liver the presence of metallothionein was below the detection limit. But, like mammalian system, chicken liver was found to contain high amount of metallothionein at neonatal stage. This naturally occurring neonatal chicken hepatic metallothionein was purified and compared with the heavy metal induced adult hepatic metallothionein. The biochemical and immunobiological comparative analysis of adult and neonatal hepatic metallothionein showed identical characteristics. The neonatal metaltothionein expressed naturally was a zinc metallothionein and unlike few other mammalian neonatal metallothionein did not contain any copper. Metallothionein was undectable in unfertilized eggs, in early embryos, and in postnatal chicken, from 4 weeks after birth. The highest level of this naturally occurring neonatal metallothionein was found in 1-4 day old neonatal liver, which was about 1.5% of the total cytosolic protein. This is the first reported evidence for the presence of ontogenically modulated expression of metallothionein in avian system. Possible biological role of neonatal metallothionein and their cellular interactions has been discussed.