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Biomedical subjects

N J Robinson

Publications and source records attributed to N J Robinson.

59 records · Page 4Linked to original sources
PubMed1987

Characterization of metal binding peptides from cadmium resistant plant cells.

The majority of the cellular cadmium (less than 80%) in cadmium resistant Datura innoxia cells is bound to a small, metal induced peptide which is not metallothionein. This peptide consists of glutamate, cysteine and glycine in a ratio between 2:2:1 and 3:3:1 and has an apparent molecular weight of 776, under denaturing conditions. It is heat stable and complexes with cadmium to produce multimeric forms which are separable by gel filtration. Chemical analyses suggest that some amino acids are not joined by classical peptide linkages. This indicates that the synthesis of the peptide may not be directed by mRNA and that induction of its synthesis may not involve increased transcription from a putative gene corresponding directly to this peptide. A smaller proportion (greater than 15%) of the cellular cadmium is bound to a larger compound which is also heat stable and binds copper more readily than cadmium in vivo. This larger compound has an amino acid composition similar, in some respects, to metallothioneins.

Amino Acids↗
PubMed1987

Poly(gamma-glutamylcysteinyl)glycine: its role in cadmium resistance in plant cells.

Angiosperms can be selected for the ability to grow in the presence of normally toxic concentrations of certain trace metal ions. Addition of Cd and Cu to Cd-resistant Datura innoxia cell cultures results in the rapid synthesis and accumulation of sulfur-rich, metal-binding polypeptides. The structure of these compounds was determined using amino acid analysis, 13C NMR, and site-specific enzymic digestion. These compounds are poly(gamma-glutamylcysteinyl)glycines. Greater than 80% of the cellular Cd is bound to the bis and tris forms in Cd-resistant cells. There is a direct correlation between the maximum accumulation of the metal-binding polypeptides and the concentration of toxic ions to which the cells are resistant. In the presence of metal ions, the polypeptides form multimeric aggregates that can be resolved by gel chromatography. Cd binds to both the high and low molecular weight aggregates, whereas Cu preferentially binds to the higher molecular weight forms. The presence of gamma-carboxamide linkages between glutamyl and adjacent cysteinyl residues indicates that these polypeptides are products of biosynthetic pathways. Poly(gamma-glutamylcysteinyl)glycines bind metals and, in this respect, appear to be functional analogs of the protein metallothionein. However, in the absence of supraoptimal concentrations of trace metal ions, the functions of metallothionein in animals and microorganisms and poly(gamma-glutamylcysteinyl)glycines in plants may differ.

Amino Acid Sequence↗
PubMedDate not supplied

Construction of Zn2+/Cd(2+)-tolerant cyanobacteria with a modified metallothionein divergon: further analysis of the function and regulation of smt.

This paper reports the (de novo) construction of mutants of Synechococcus PCC 7942 lacking the repressor (SmtB) of the metallothionein gene, smtA. These smtA+/B- cells are more tolerant to elevated [Zn2+] and [Cd2+] than cells containing an intact metallothionein divergon (smt). Previously selected (by step-wise adaptation) Cd(2+)-tolerant mutants contain additional copies of smtA and possibly other undetected mutations. It is now confirmed that these cells also contain a deletion within 'all' copies of smtB and hence fail to revert to wild type following subculture in medium which has not been supplemented with Cd2+ or Zn2+. Northern analysis showed enhanced accumulation of smtA transcripts, even in the absence of added metal ions in these mutants. An increase in the accumulation of Zn2+ is reported in cells containing an intact metallothionein divergon compared to cells deficient in both smtA and smtB. This supports the assumption that SmtA binds Zn2+ within cyanobacterial cells. We also describe the use of the above mentioned mutants to identify additional factors involved in the regulation of transcription from the smtA operator-promoter.

Bacterial Proteins↗