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R K Gupta

Publications and source records attributed to R K Gupta.

At least 829 records · Page 46Linked to original sources
PubMed1970

Double nuclear magnetic resonance observation of electron exchange between ferri- and ferrocytochrome c.

Cyanide-inhibited electron exchange between ferri- and ferrocytochrome c molecules has been observed by nuclear magnetic resonance. Irradiation of a partially reduced protein solution at resonance frequencies arising from protons of the oxidized state results in a decrease in the absorption due to the corresponding protons of the reduced state. The experiment quantitates the hyperfine shifts observed in this system and can be used to identify hitherto unassignable resonances. Analysis of the shifts suggests that an aromatic side chain ring lies near the edge of the heme ring.

Cytochromes↗
PubMed1970

Amino acid transport by the filamentous fungus Arthrobotrys conoides.

Uptake of l-valine by germinated spores of Arthrobotrys conoides has all the characteristics of a system of transport that requires an expenditure of energy by the cells. It is dependent on temperature and has an energy of activation of 16,000 cal/mole. Uptake is optimal at pH 5 to 6. l-Valine accumulated against a concentration gradient and is not lost from the cells by leakage or exchange. The process requires energy supplied by the metabolic reactions that are inhibited by catalytic amounts of 2,4-dinitrophenol and azide. The kinetics of the system are consistent with a mechanism of transport that depends on a limited number of sites on the cell surface, and the Michaelis constant for the system is 1.5 x 10(-5) to 7.5 x 10(-5)m. Modification of the amino or carboxyl group abolishes l-valine uptake. The process is competitively inhibited by d-valine, glycine, and other neutral amino acids (K(i) = 1.5 x 10(-5) to 4.0 x 10(-5)m), indicating a lack of stereospecificity, and also indicating that aliphatic side chain is not required for binding with the carrier. The transport system has less affinity for acidic amino acids (glutamic and aspartic acids) than neutral amino acids, and a greater affinity for basic amino acids (histidine, lysine, and arginine). The range of affinity is in the order of 100, as measured in terms of K(i) values for various compounds. The data presented provide suggestive evidence that the uptake by A. conoides of all amino acids except proline is mediated by a single carrier system that possesses an overall negative charge.

Amino Acids↗
PubMed1970

Metabolism of valine by the filamentous fungus Arthrobotrys conoides.

Uptake of valine by Arthrobotrys conoides was an active process and was independent of its incorporation into cellular protein. Chemical fractionation of cells supplied with (14)C-l-valine for different time intervals revealed that the amino acid initially entered a pool of metabolic intermediates and was extractable with cold trichloroacetic acid. After a 4-min interval, some intracellular valine was incorporated into cell proteins, but most underwent metabolic transformation to a variety of products that included carboxylic acids and other amino acids. Carbon derived from valine was not localized in the lipid or nucleic acid fraction of cells, but some was completely oxidized and recovered as metabolic (14)CO(2). Autoradiograms of paper and thin-layer chromatograms of acid hydrolysates of cellular protein identified the following amino acids as having originated from valine: glutamate, aspartate, alanine, and leucine. Similar analysis of cold trichloroacetic acid extracts established that (14)C supplied as l-valine had been transformed also to alpha-ketoisovalerate, isobutyrate, propionate, succinate, malate, oxalacetate, pyruvate, and alpha-ketoglutarate. Pathways for transformation of the carbon skeleton of valine to various metabolic products are proposed.

Alanine↗