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Biomedical subjects

R Becker

Publications and source records attributed to R Becker.

At least 271 records · Page 15Linked to original sources
PubMed1976

Hydrogen production in the rat following ingestion of raffinose, stachyose and oligosaccharide-free bean residue.

Raffinose and stachyose were compared to cooked California Small White beans (CSW) containing 4% alpha-oligosaccharides (stachyose and raffinose) and to oligosaccharide-free CSW solids (residue from hexane and 70% ethanol extraction of CSW) as sources of hydrogen when ingested by rats maintained in life support systems. If the oligosaccharide content were the only hydrogen source in CSW, it would have had to be 25 times as potent as CSW, but raffinose was only five times and stachyose seven times as potent as CSW. Oligosaccharide-free residue was 0.4 to 0.5 as active as CSW. Hydrogen producing potencies of stachyose and raffinose were enhanced by feeding in combinations with residue. The increases in hydrogen production from the combinations were more than additive. Thus, CSW contains at least one 70% alcohol-insoluble substance which, in addition to the oligosaccharides, is essential to bring about quantitatively the physiological response to whole beans observed in rats.

Animals↗
PubMed1975

Modulation of the enzymic activity of chicken pepsin by the covalent modification of its single -- SH group.

The single cysteinyl residue of chicken pepsin was modified with a wide spectrum of reagents to produce mixed disulfides or alkylated derivatives. All these derivatives showed enhanced catalytic activity towards the synthetic peptide Z-Ala-Ala-Phe-OPrP, where OPrP is the 3-(4-pyridyl)-propyl-1-oxy group. The overall catalytic constant kcat/Km for these derivatives was 4 -- 25-fold larger than that of the native enzyme. The activity of the enzyme towards denatured hemoglobin was slightly decreased (10--45%) by these modifications. When the mixed disulfide derivatives were treated with excess mercaptan, the sulfhydryl group was regenerated and activity reverted to that of the native enzyme. The --SH group of chicken pepsin reacted preferentially with reagents containing an aromatic group. The reaction was found to depend on the ionization of a single group, presumably the --SH itself, with a pKa = 7.5. The rate of reaction of the fully deprotonated species with various disulfides was 100--1000-fold smaller than that of the --SH group of glutathione. It is suggested that the groups attached covalently to the sulfhydryl also interact with other amino acid side chains in the protein thereby affecting the active center of chicken pepsin.

Amino Acids↗
PubMed1975

Solubilization of the Semliki Forest virus membrane with sodium dodecyl sulfate.

The dissociation of Semliki Forest virus induced by increasing concentrations of the anionic detergent sodium dodecyl sulfate was studied using density gradient centrifugation. Detectable binding to the virus started well below the critical micellar concentration of the detergent and increased thereafter with increased detergent concentration. At 4 degrees there were about 11,000 binding sites per virus particle with an average association constant of about 10-5 M-1. The extent of virus dissociation could be controlled both by the detergent concentration and by the temperature. At 4 degrees only disruption ("lysis") of the virus membrane could be observed. At 20 degrees most of the membrane was solubilized into lipoprotein complexes, and the nucleocapsid dissociated into RNA and protein. Complete delipidation of the viral membrane proteins was achieved at 30 degrees at a detergent concentration still below the critical micellar concentration.

Binding Sites↗