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Biomedical subjects

M J McKay

Publications and source records attributed to M J McKay.

47 records · Page 3Linked to original sources
PubMed1983

Action of human liver cathepsin B on the oxidized insulin B chain.

The lysosomal cysteine proteinase cathepsin B (from human liver) was tested for its peptide-bond specificity against the oxidized B-chain of insulin. Sixteen peptide degradation products were separated by high-pressure liquid chromatography and thin-layer chromatography and were analysed for their amino acid content and N-terminal amino acid residue. Five major and six minor cleavage sites were identified; the major cleavage sites were Gln(4)-His(5), Ser(9)-His(10), Glu(13)-Ala(14), Tyr(16)-Leu(17) and Gly(23)-Phe(24). The findings indicate that human cathepsin B has a broad specificity, with no clearly defined requirement for any particular amino acid residues in the vicinity of the cleavage sites. The enzyme did not display peptidyldipeptidase activity with this substrate, and showed a specificity different from those reported for two other cysteine proteinases, papain and rat cathepsin L.

Binding Sites↗
PubMed1983

Subcellular distribution of abnormal proteins in rabbit reticulocytes. Effects of cellular maturation, phenylhydrazine and inhibitors of ATP synthesis.

Inhibitors of ATP synthesis (cyanide, dinitrophenol, fluoride) inhibited proteolysis of pulse-labelled abnormal proteins in rabbit reticulocytes and caused an accumulation of the aberrant polypeptides in the cell debris fraction in a manner analogous to phenylhydrazine-induced Heinz bodies. When the reticulocytes were separated into age-groups by sedimentation through discontinuous gradients of bovine serum albumin, the ability of the cells to degrade puromycin peptides decreased with increasing cellular maturity and, in the more mature cells, up to 40% of the labelled abnormal polypeptide remained associated with the cell debris fraction at the end of the chase period. It is suggested that the association of the abnormal polypeptide with the cell debris fraction is a consequence of a maturation-induced loss, or an inhibitor-induced inactivation of the cellular proteolytic activity.

Adenosine Triphosphate↗
PubMed1983

Protease and peptidase activities during reticulocyte maturation.

Rabbit reticulocytes were fractionated according to buoyant density on albumin gradients. The properties of fractionated cells were consistent with the thesis that the procedure separated the reticulocytes according to their degree of maturation. Catabolism of aminoethylcysteine-induced abnormal protein and puromycin-peptides declined with increasing cellular maturity. Cell-free extracts showed a similar decrease in degradative activity: addition of extracts of young cells stimulated proteolysis in extracts from old cells. Peptidase activity also declined during maturation. In the more mature cells abnormal protein was located increasingly in the cell-debris fraction, analogous to Heinz bodies.

Animals↗
PubMed1982

Effects of ATP and cell development on the metabolism of high molecular weight aggregates of abnormal proteins in rabbit reticulocytes and cell-free extracts.

Abnormal proteins synthesized in rabbit reticulocytes in response to (i) the lysine analogue aminoethylcysteine and (ii) puromycin, form high molecular weight aggregates prior to degradation. Inhibitors of ATP synthesis partially inhibit catabolism of the aminoethylcysteine-induced abnormal protein; degradation of puromycin peptides synthesized after incubation with 25 micrograms/ml puromycin was not inhibited. Catabolism of the analogue-induced high molecular weight aggregate of abnormal protein in cell-free extracts was markedly stimulated by ATP, whereas proteolysis of the aggregated puromycin-peptides was ATP-independent. The ability of the reticulocytes to degrade the puromycin-peptide aggregates was found to decrease with cellular maturity. It is suggested that the energy-dependency for proteolysis is in some way related to the chain length of the abnormal protein synthesized.

2,4-Dinitrophenol↗
PubMed1982

ATP-independent proteolysis of globin cyanogen bromide peptides in rabbit reticulocyte cell-free extracts.

The catabolism of two rabbit globin cyanogen bromide peptides in cell-free extracts of ATP-depleted rabbit reticulocytes has been studied. Proteolysis of the peptides (3533 and 5957 molecular weight) proceeded rapidly in the absence of ATP, had a pH optimum of approximately 7.8, and was inhibited by omicron-phenanthroline, N-ethylmaleimide, cystamine zinc and cobalt ions, and puromycin peptide high-molecular-weight aggregates. Proteolysis of puromycin peptides was inhibited by the rabbit globin cyanogen bromide peptides. The ability of cell-free extracts of degrade the globin cyanogen bromide peptides decreased with the reticulocyte maturity. Blocking the globin cyanogen bromide peptide amino groups by succinic and maleic anhydride treatment decreased susceptibility to degradation. It is suggested that the globin cyanogen bromide peptides might provide model substrates, replacing puromycin peptides, for the investigation of ATP-independent proteolytic events.

Adenosine Triphosphate↗
PubMed1981

Selective proteolysis of abnormal proteins of shortened chain length in rabbit reticulocytes.

Proteolysis of certain shortened globin chains can proceed in cell-free extracts of rabbit reticulocytes in the absence of ATP. Proteolysis of amino acid analogue-induced abnormal globin chains of normal chain length may be stimulated by ATP, however. The ATP independent degradation of globin cyanogen bromide-peptides appears to require the presence of free, unblocked amino groups in the substrate, has a pH optimum of 7.8 and is inhibited by phenanthroline, cobalt and zinc ions, N-ethylmaleimide and cystamine.

Adenosine Triphosphate↗
PubMed1980

Breakdown of aberrant protein in rabbit reticulocytes decreases with cell age.

Rabbit reticulocytes, separated into ten cell age groups by bovine serum albumin density-gradient sedimentation, were pulse-labelled with [14C]leucine in the presence of either puromycin dihydrochloride or aminoethyl-L-cysteine (a lysine analogue). Intracellular proteolysis of both the puromyucinyl-peptides and analogue-containing protein decreased with cell maturity.

Animals↗