Pigeon metallothionein consists of two species

Lih yuan Lin, W. C. Lin, P. C. Huang

Research output: Contribution to journalArticlepeer-review

Abstract

Two isospecies of metallothionein, a cysteine-rich protein that binds metals, exist in all mammals examined, but only one in some invertebrates and lower animals. Lower vertebrates such as fish and birds have one or two metallothionein genes depending upon the organism. In this study, we show by amino acid sequence determinations that two isospecies of metallothionein, 75% homologous to each other, can be induced by zinc to accumulate in pigeon livers. This is in contrast to single isospecies found in chicken and duck. Each of these two sequences consists of 63 amino acids, with all 20 cysteines in positions held invariant in most if not all class I mammalian metallothioneins. One of these two pigeon isometallothioneins is terminated with histidine at the carboxyl end, which is apparently unique to avians. Its sequence differs from that of duck and chicken by only four substitutions and is the predominant isospecies that accumulates upon induction. The other pigeon metallothionein has lysine at its carboxyl terminus and is devoid of arginine. None of these isospecies carries any aromatic amino acid, which is also characteristic of all higher metallothioneins. As this is the first demonstration with sequence data that two isospecies of metallothionein indeed exist in birds, these results suggest that pigeon metallothionein genes evolved from an ancestral form through duplication and mutation upon specification.

Original languageEnglish (US)
Pages (from-to)248-255
Number of pages8
JournalBiochimica et Biophysica Acta (BBA)/Protein Structure and Molecular
Volume1037
Issue number2
DOIs
StatePublished - Feb 9 1990

Keywords

  • (Pigeon)
  • Enzyme induction
  • Isoenzyme
  • Metallothionein
  • Zinc

ASJC Scopus subject areas

  • Biophysics
  • Structural Biology
  • Biochemistry
  • Molecular Biology

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