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W S Champney

Publications and source records attributed to W S Champney.

43 records · Page 3Linked to original sources
PubMed1970

Molecular events in the growth inhibition of Bacillus subtilis by D-tyrosine.

The transformable strain of Bacillus subtilis strain 168 is extremely susceptible to growth inhibition by d-tyrosine. The molecular events associated with the inhibition of growth by d-tyrosine in this strain include the false feedback inhibition and probably the false repression of prephenate dehydrogenase. These effects were found to contribute to the formation of d-tyrosine-containing proteins by decreasing the intracellular concentration of l-tyrosine. Accordingly, growth inhibition of strain 168 by the d isomer of tyrosine was shown to be progressive, enduring, and delayed by prior growth on l-tyrosine. The synthesis of cellular macromolecules and viable cell count were progressively diminished in d-tyrosine-inhibited cultures. Several different enzyme activities were reduced after growth in the presence of d-tyrosine. Isotopic d-tyrosine was incorporated into cellular proteins without change of optical configuration. Long chains of cells with completed septa were observed microscopically, and therefore some cell wall effect may also be implicated.

Bacillus subtilis↗
PubMed1970

Metabolic influences on tyrosine excretion in Bacillus subtilis.

The biosynthetic pathway for tyrosine synthesis is regulated both by repression of enzyme synthesis and by feedback inhibition of enzyme activity in Bacillus subtilis. Nevertheless, wild-type cells produce significantly more tyrosine than is required for protein synthesis, and part of this is excreted into the medium. Alteration of nutritional and other environmental conditions of cultivation strongly influenced the amount of tyrosine excretion. The excretion of tyrosine by wild-type cells was compared with that of a regulatory mutant having a feedback-insensitive prephenate dehydrogenase. Tyrosine excretion varied directly with the in vitro activity of prephenate dehydrogenase and inversely with temperature in the two strains. The regulatory mutant excreted five times as much tyrosine as the wild type at all growth temperatures examined. The carbon source used for growth significantly influenced the level of tyrosine excretion. The specific activity of prephenate dehydrogenase was also affected by the carbon source. Incorporation studies with isotopic tyrosine and fluorometric determinations of tyrosine concentrations extractable in hot water were used to measure operationally the tyrosine pools in the mutant and wild-type strains. The effects of various environmental conditions on the synthesis and excretion of tyrosine led to the conclusion that metabolic controls governing end product contrations exist which are completely independent of regulation by feedback inhibition and repression.

Bacillus subtilis↗
PubMed1969

D-Tyrosine as a metabolic inhibitor of Bacillus subtilis.

The d-isomer of tyrosine is a potent inhibitor of growth in transformable strain 168 of Bacillus subtilis. A d-tyrosine-resistant mutant of the inhibited strain was isolated which excreted l-tyrosine, had a diminished growth rate, and required l-phenylalanine to attain the growth rate of the wild-type parent. Mapping by deoxyribonucleate transformation located this resistance in the gene coding for prephenate dehydrogenase. This enzyme in the d-tyrosine-resistant mutant was insensitive to the usual feedback inhibition exerted by l-tyrosine in extracts of strain 168. In contrast, the growth of poorly transformable strain 23 of B. subtilis, as well as that of several other Bacillus species, was not affected by the analogue. Transformation mapping demonstrated no linkage of this latter "natural resistance" to several different aromatic markers. Prephenate dehydrogenase in extracts from strain 23 was as sensitive as that from strain 168 to feedback inhibition by l-tyrosine in vitro. The relationships of the latter results to the regulation of tyrosine biosynthesis and the possible nature of strain differences in d-tyrosine sensitivity are discussed.

Bacillus subtilis↗
PubMedDate not supplied

A rapid method for the purification of RNA polymerase holoenzyme from Escherichia coli.

A method is described for the rapid purification of RNA polymerase holoenzyme from small amounts of Escherichia coli cells. Chromatography of a crude extract on a single-stranded DNA agarose column followed by gel filtration chromatography gave 95% pure holoenzyme. The enzyme had kinetic characteristics on T7 DNA identical to those of RNA polymerase purified by other more laborious procedures.

Chromatography, Affinity↗