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Biomedical subjects

R C Valentine

Publications and source records attributed to R C Valentine.

At least 37 records · Page 2Linked to original sources
PubMed1972

Adenosine 3':5'-cyclic monophosphate control of the enzymes of glutamine metabolism in Escherichia coli.

The effect of cAMP on the intracellular levels of five enzymes concerned with the interconversion of glutamate and glutamine in E. coli has been examined. Cyclic AMP added to the culture medium increases the levels of glutamate dehydrogenase (EC 1.4.1.4) and glutamine synthetase (EC 6.3.1.2); it decreases the levels of glutamate synthase (EC 1.4.1.X), and glutaminase A (EC 3.5.1.2). Cyclic AMP did not affect the level of glutaminase B (EC 3.5.1.2). These alterations in enzyme levels by cAMP require cyclic AMP receptor protein, since the levels of these enzymes were unchanged by cAMP in a mutant lacking this receptor. Chloramphenicol also abolished the effects of cAMP, a result that implies protein synthesis is necessary for these changes in enzyme levels to occur. The reciprocal effects of cAMP on the levels of these enzymes may play an important role in the cellular regulation of nitrogen metabolism.

Adenylyl Cyclases↗
PubMed1972

Four-iron (sulfide) ferredoxin from Bacillus polymyxa.

Ferredoxin from Bacillus polymyxa contains (per mole) four non-heme iron residues, four acid-labile sulfide residues, and four cysteine residues. Its molecular weight is approximately 8,800, and it has an oxidation-reduction potential (E(m)) of -390 mv. It is active as an electron carrier in several ferredoxin-linked enzyme systems.

Amino Acids↗
PubMed1971

The use of bifunctional biotinyl compounds to determine the arrangement of subunits in avidin.

A series of bisbiotinyl diamines was synthesized with between 9 and 25 bonds between the carboxyl groups of the two biotin residues. It was found that only one of the two biotin residues could combine with avidin when there were fewer than 12 bonds between the biotin residues. Compounds with longer chains behaved in a bifunctional manner and gave rise to linear polymers of avidin, which were characterized by electron microscopy and by gel filtration. The polymers formed with the shorter-chain reagents (12, 13 or 14 bonds) were relatively unstable and could be depolymerized by weakly bound analogues of biotin. The polymers of longer-chain reagents were not depolymerized under these conditions and were only slowly affected by added biotin. When the chain length of the reagent reached 23 bonds the polymers became much shorter, suggesting that the reagent was now able to link two subunits within the same avidin molecule. From the morphology of the polymers it could be concluded that the four subunits of the avidin molecules were arranged with 222 symmetry and that they were grouped in two pairs at opposite ends of the short axis of the molecule whose dimensions were 55Ax55Ax41A.

Binding Sites↗
PubMed1971

Transduction of the nitrogen-fixation genes in Klebsiella pneumoniae.

The bacteriophage P1 infects and functions as a generalized transducing phage for nitrogen-fixing strains of the coliform bacterium Klebsiella pneumoniae. Bacterial mutants (nif(-)) unable to grow on molecular nitrogen as a nitrogen source were found to be deficient in nitrogenase activity as assayed by the conversion of acetylene to ethylene. These mutants regained normal nitrogenase activity and the ability to grow on N(2) after transduction with lysates of P1 phage prepared from wild-type bacteria. Transductional analysis with P1 revealed that several nif genes are located on the genetic linkage map of Klebsiella near the histidine operon.

Anaerobiosis↗
PubMed1969

The electron transport system in nitrogen fixation by Azotobacter. I. Azotoflavin as an electron carrier.

A flavoprotein, named azotoflavin, was isolated from an extract of Azotobacter vinelandii cells, which linked the reducing power generated by illuminated spinach chloroplasts to the Azotobacter nitrogen-fixing enzyme complex. The photoreduction of the yellow azotoflavin by chloroplasts produced a stable, free-radical semiquinone, blue in color, with properties similar to those described by other investigators for an Azotobacter flavoprotein of unknown biological function.

Azotobacter↗
PubMed1969

Virus structure.

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DNA, Viral↗