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Biomedical subjects

R C Valentine

Publications and source records attributed to R C Valentine.

At least 19 recordsLinked to original sources
PubMed1984

Molecular biology of osmoregulation.

The drought of 1983 resulted in some 10 billion dollars in agricultural losses and has focused attention on the vulnerability of our major crops to this devastating form of environmental stress. This article is concerned with the molecular biology of a new class of genes, called osm (osmotic tolerance) genes, that protect bacteria like Escherichia coli against osmotic stress and may work in a similar manner in plants and animals. Osm genes govern the production of a class of molecules, such as betaine and proline, that protect the cell and its constituents against dehydration. These osmoprotectant molecules have been known for many years to accumulate in plants but have only recently been shown to have potent antistress activity for bacteria.

Adaptation, Physiological↗
PubMed1975

Energy requirements for biosynthesis of DNA in Escherichia coli. Role of membrane-bound energy-transducing ATPase (coupling factor).

A mutant of Escherichia coli missing energy-transducing ATPase and known to be defective in a variety of membrane functions from earlier studies (Yamamoto, T. H., Mével-Ninio, M. and Valentine, R. C. (1973) Biochim. Biophys. Acta 314, 267-275; Thipayathasana, P. and Valentine, R. C. (1974) Biochim. Biophys. Acta 347, 464-468; Mével-Ninio, M. and Yamamoto, T. (1974) Biochim. Biophys. Acta 357, 63-66) has been found to be blocked for anaerobic DNA synthesis. The rate of anaerobic DNA synthesis in the mutant, measured as radioactive adenine incorporation into the alkali-resistant fraction of whole cells, is about 1/6 the rate of DNA synthesis in the wild type culture under similar conditions. Addition of NO-3- or O-2 restores DNA biosynthesis in the mutant. The entry of radioactive adenine is not appreciably affected in the mutant by anaerobiosis. It is concluded that coupling factor plays a role in some step(s) of DNA biosynthesis.

Adenine↗
PubMed1975

Microbial production of ammonium ion from nitrogen.

Genetic manipulation of nitrogenase and key glutamate-forming enzymes can provide mutants that excrete fixed N2 as NH4+. A derepressed N2 fxation mutant (SK-24) has been isolated , which excretes up to 20.2 mumol of fixed N2 as NH4+ per mg of cell protein in 24 hr at room temperature. Biochemical analysis shows that this mutant, which requires glutamate for growth, releases fixed N2 as NH4+ into the environment because of (i) constitutive synthesis of nitrogenase and (ii) genetic blocks resulting in losses of glutamate synthase [L-glutamine:2-oxoglutarate aminotransferase (NADPH oxidizing), EC 2.6.1.53] and glutamate dehydrogenase [L-glutamate:NADP oxidoreductase (deaminating), EC 1.4.1.4] activities, enzymes essential for NH4+ assimilation into cell material. The parent strain (asm-1), missing only glutamate synthase activity, also actively excretes NH4+ during early phases of its growth but eventually reutilizes the NN4+. A miximum yield of 4.0 mumol of NH4+/ml per 24 hr has been noted for asm-1 only during the growth period. Biosynthesis of NH4+ PROCEEDS AT THE EXPENSE OF A Variety of fermentable sugars, such as sucrose or glucose, with a maximum energy conversion efficiency of about 5 glucose degraded per NH4+ formed. The use of microbes for production of NH4+ fertilizer is discussed.

Ammonia↗