Biomedical subjects

M G Beyer

Publications and source records attributed to M G Beyer.

4 recordsLinked to original sources

PubMed1976

Activation of pepsin (EC 3.4.4.1) by heavy-metal ions including a contribution to the mode of action of copper sulphate in pig nutrition.

1. Kinetic experimetns were done with pepsin (EC 3.4.4.1) using haemoglobin as a substrate in the presence of different metal cations. 2. The activation of peptic hydrolysis with higher concentration of cupric ions added to the reaction mixture was determined from turnover-rate curves in experiments with constant substrate concentration. With a Cu2+ concentration greater than 1.67 X 10(-4) M activation was obtained. 3. Nickel ions at a concentration of 8-33 X 10(-4) M and at higher concentrations also increased pepsin activity. Additions of ferrous ions and zinc ions had no effect. 4. Experiments were done using variable substrate concentrations in the presence of different Cu2+ concentrations. The concentrations of haemoglobin ([S]) at half maximum velocity were determined. The double-reciprocal plots of [S] v. reaction velocity (v) (i.e. 1/[S] v. 1/v) had no common intersection point. Therefore the kinetics did not correspond to any of the known kinetics. The activation brought about by Cu2+ cannot easily be explained by the study of the kinetics. Certain simple explanations of the phenomenon can be eliminated.

Animal Nutritional Physiological Phenomena↗

PubMed1976

[Interactions between various transition elements in their effect on pepsin activity].

Kinetic experiments were made with pepsin in the presence of Cu2+ ions and additional Fe2+, Ni2+ or Zn3+ ions as sulphates. As a parameter of the pepsin activity the turnover-rate curves were determined with haemoglobin as a substrate. An important activation of the pepsin was obtained by Cu2+ additions of 5-10(-4) mole/1. When Cu2+ and Fe2+ ions were added to the reaction mixture at the same time, an additive effect of both metal cations was observed. A competitive effect of both metal cations was found in the combination of Cu2+/Ni2+ ions. Zn2+ addition did not influence the activation of pepsin caused by Cu2+ ions.

Animals↗

PubMed1976

[The effect of various pH values on in vitro peptic digestion of proteins in the presence of Cu2 ions].

Studies were carried out to investigate the effect of different pH values on the peptic digestion of soya protein in the presence and in the absence of Cu2+ ions. The studies were performed in vitro at a pH of 2.2 and 3.2, with 2.96 X 10(-5) mole of Cu2+ ions present in 11 of the reaction mixture. The reaction was carried out in a digestion apparatus permitting dialysis of the cleavage products. Different parameters were used as criteria of digestion, viz. the quantity of N contained in the reaction vessel (residue) and in the resulting dialysis products as determined by Kjehldahl microanalysis and automatic amino acid analysis, the proportions of digestion products found in the different molecular ranges after partition of Sephadex G 75 and the composition of amino acids in the cleavage products. From the distribution of the reaction products on the residue and dialysis products and on the different molecular ranges it was found that additions of Cu2+ ions at pH 2.2 produced a considerable inhibition of digestion. With a rise in pH to 3.2 peptic digestion decreased even without the addition of Cu2+. Supplementation of Cu2+ ions produced only a slight additional effect in the molecular range termed "exclusion limit". In the case of the amino acids tyrosine and phenylalanine it was found that an increase in pH changed the composition of peptides within the different molecular ranges. Additions of Cu2+ had no influence on the amino acid composition.

Copper↗

PubMed1975

[On the complex formation of proteins with cu ions under acidic conditions].

In order to determine the influence of copper additives on the protein digestibility, the complex formation of proteins with Cu ions under acidic conditions (pH=2.2) was investigated. Isolated soja-protein (300 mg) resp. pepsin was mixed with 10 mumol (2.49 mg) CuSO4-5H2O and dialysed against low molecular complexing agents with increasing affinity towards copper ions. The experiments with soja-protein showed, that most of the Cu ions dialysed (97% of total Cu2+ content) without any addition of complexing agents, pepsin, however, had a lower percentage (83% of total Cu2+ content). The remaining copper ions in pepsin could only be removed by alanin and ammonium-tetramethylendithiocarbamate. Therefore it is concluded, that in the acidic range Cu ions only form complexes with pepsin, but not with soja-protein. This effect is due to the very low isoelectric point of pepsin. The determination of iron, nickel, and zinc in native proteins revealed, that at pH=2.2 iron and nickel are stronger linked to pepsin than to soja-protein; only zinc was loosely bound to both proteins.

Copper↗