US EPA

8178325 

Journal Article 

Preparation and properties of the major copper-binding component in human fetal liver. Its identification as metallothionein 

Ryden, L; Deutsch, HF 

1978 

Yes 

Journal of Biological Chemistry
ISSN: 0021-9258
EISSN: 1083-351X 

253 

2 

519-524 

English 

Most of the relatively large amounts of copper in human fetal liver is bound to a low molecular weight protein. Extraction with solutions containing 2-mercaptoethanol permits solubilization of approximately 75% of the copper of homogenates without any apparent influences on the major binding component or loss of its metal. By a combination of gel filtrations and covalent chromatography on thiopropyl-Sepharose the monomeric form of the copper-binding protein and some polymers of it were prepared in good yield. It could be resolved into several components by chromatography on DEAE-Sephadex. The protein was identified as a copper-thionein by the criteria of molecular weight, shape, amino acid composition, and amino acid sequence homology. Gel filtration in 6 M quanidine-HCI showed that the molecule was a single peptide chain of 58 residues, corresponding to a molecular weight of 6000. Gel filtration experiments in dilute buffers gave a molecular weight of 9500 which suggests that the molecule should be more asymmetric than the globular proteins employed as standards. An approximate frictional ratio of 1.40 was calculated from these data. Its amino acid composition was very similar to that of the zinc-binding metallothionein previously isolated from adult human liver, but the cysteine content is somewhat lower. The amino acid sequence following the single methionine residue was closely homologous to that of zinc-binding metallothionein from horse kidney. The protein contained 2.4 g atoms of copper/mol and traces of manganese and zinc, but no cadmium. The copper was not paramagnetic. Possible roles of this copper-binding protein in the transport and storage of copper are discussed.