Biomedical subjects

E E Snell

Publications and source records attributed to E E Snell.

At least 109 records · Page 6Linked to original sources

PubMed1971

Vitamin B 6 -responsive histidine deficiency in mutants of Salmonella typhimurium.

A mutant of Salmonella typhimurium LT-2 that requires either vitamin B(6) or histidine for growth was found to synthesize vitamin B(5) in amounts comparable to the parent strain, but to be deficient in imidazoleacetol phosphate transaminase (L-histidinolphosphate: 2-oxoglutarate aminotransferase, EC 2.6.1.9), an enzyme required for histidine biosynthesis. The mutant apotransaminase required a 50-fold higher concentration of pyridoxal 5'-phosphate for half-maximum activation than the corresponding wild-type enzyme; the fully activated mutant enzyme also displays a much lower maximum rate of catalysis than the enzyme from the parent strain. Such mutational changes in bacteria resemble those in certain vitamin B(6)-responsive genetic diseases in man and provide useful experimental material for the study of factors involved in coenzyme binding and enzymatic catalysis.

Catalysis↗

PubMed1971

Salmonella typhimurium mutants with alternate requirements for vitamin B 6 or isoleucine.

Several mutants of Salmonella typhimurium LT-2, isolated as auxotrophs for vitamin B(6), grew without the added vitamin when supplied with either isoleucine, alpha-ketobutyrate, or alpha-keto-beta-methylvalerate, but not with threonine or with other alpha-keto acids. When grown on minimal medium supplemented with isoleucine, these mutants synthesized vitamin B(6) in amounts comparable to wild-type cells; they thus appeared to contain a modified l-threonine dehydratase and to belong to genotype ilvA (threonine dehydratase) instead of pdx (pyridoxine). Direct assays confirmed this hypothesis. Wild-type cells (toluene-treated) showed approximately the same threonine dehydratase activity whether grown in the presence or absence of added pyridoxal-P; mutant cells approached the activity of wild-type cells only when they were grown with added vitamin B(6) and were assayed in the presence of pyridoxal-P. In cell-free extracts, the threonine dehydratase from mutant cells was cold labile and more labile to oxidative inactivation than the wild-type enzyme; furthermore, activation of the mutant apoenzyme required a 10- to 20-fold higher concentration of pyridoxal-P than was required for the wild-type apoenzyme. These results show that cultures which appear auxotrophic for a given vitamin may synthesize that vitamin in normal amounts, the exogenous requirement arising from impaired binding of the vitamin-derived coenzyme to a genetically altered apoenzyme dependent on that coenzyme. Inadequate nutritional data to support the genetic findings can lead to erroneous genotype classification for such mutants.

Amino Acids↗

PubMed1971

Growth characteristics of a pseudomonad which utilizes pyridoxine or pyridoxamine as a carbon source.

Cultural characteristics of Pseudomonas MA-1, which has been extensively used as a source of enzymes that degrade vitamin B(6), confirm its classification as a pseudomonad. The organism requires biotin for growth; any one of several amino acids is also required for growth when pyridoxine (but not when glucose) serves as the energy source. Growth of Pseudomonas MA-1 is inhibited by one or more unidentified substances formed when pyridoxine is autoclaved with the medium. Modified cultural conditions are described which permit the large-scale growth of the organism with pyridoxine as carbon source.

Amino Acids↗

PubMed1970