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J R Fincham

Publications and source records attributed to J R Fincham.

53 records · Page 3Linked to original sources
PubMed1970

Regulation of nitrate reductase in the basidiomycete Ustilago maydis.

Nitrate reductase was induced in Ustilago maydis by growth in medium containing only nitrate as the nitrogen source. Ammonium ions repressed the enzyme and led to a rapid loss of activity. Ammonium did not inhibit the enzyme in vitro; although amino acids partially did so, this cannot account for the rapid loss of in vivo activity which occurred when the ammonium was added. Experiments with cycloheximide and actinomycin D, together with measurements of protein turnover, suggested that nitrate reductase is actively broken down when cells with fully induced activity are transferred to medium containing ammonium ions.

Basidiomycota↗
PubMed1970

Fungal genetics.

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Amino Acid Sequence↗
PubMed1968

Acetate-onutilizing mutants of Neurospora crassa. I. Mutant isolation, complementation studies, and linkage relationships.

Sixty mutants of Neurospora crassa unable to grow on acetate as sole source of carbon, but able to utilize sucrose, were isolated. On the basis of complementation tests, they were divided into seven groups, each group representing a different gene. Six of the genes have been mapped; no two are closely linked. These loci have been designated acu-1 to acu-7. Mutations at four of these loci result in poor germination of ascospores.

Acetates↗
PubMed1968

Acetate-nonutilizing mutants of Neurospora rassa. II. Biochemical deficiencies and the roles of certain enzymes.

The levels of Krebs cycle, glyoxylate cycle, and certain other enzymes were measured in a wild-type strain and in seven groups of acetate-nonutilizing (acu) mutants of Neurospora crassa, both after growth on a medium containing sucrose and after a subsequent 6-hr incubation in a similar medium, containing acetate as the sole source of carbon. In the wild strain, incubation in acetate medium caused a rise in the levels of isocitrate lyase, malate synthase, phosphoenolpyruvate carboxykinase, acetyl-coenzyme A synthetase, nicotinamide adenine dinucleotide phosphate-linked isocitrate dehydrogenase, citrate synthase, and fumarate hydratase. Isocitrate lyase activity was absent in acu-3 mutants; acu-5 mutants lacked acetyl-coenzyme A synthetase activity; and no oxoglutarate dehydrogenase activity (or only low levels) could be detected in acu-2 and acu-7 mutants. In acu-6 mutants, phosphoenolpyruvate carboxykinase activity was either very low or absent. No specific biochemical deficiencies could be attributed to the acu-1 and acu-4 mutations. The role of several of these enzymes during growth on acetate is discussed.

Acetates↗
PubMed1968

Nature of the complementation products formed by a complementing mutant of neurospora crassa.

The mutant am-14 produces no active nicotinamide adenine dinucleotide phosphate-linked glutamate dehydrogenase (GDH) and no protein showing immunological cross-reaction with the enzyme. Nevertheless, it shows complementation with several other am mutants in heterokaryons. Active GDH can be extracted from heterokaryons formed from am-14 and other mutants which, by themselves, produce more or less inactive varieties of the enzyme. The enzyme from am-14 + am-3 heterokaryons can be partially separated from am-3 mutant GDH on a diethylaminoethyl cellulose column. It is characterized by abnormally high thermolability and by a capacity for activation by glutamate. By the same procedure as brings about hybridization between mutant GDH proteins, it has been possible to recover enzyme with the properties of pure am-3 GDH from a partially purified am-14 + am-3 GDH preparation which was initially substantially free of unhybridized am-3 enzyme. This is interpreted as evidence that the active complementation product is a hybrid oligomer containing am-3 monomers and also am-14 monomers, the latter being unable to aggregate by themselves. Heterokaryons formed from am-14 and wild type produce GDH of abnormally high thermolability, presumably due to the formation of am-14 + am(+) hybrids.

Alleles↗
PubMed1967

Effects of pH and temperature on the wild-type and a mutant form of Neurospora glutamate dehydrogenase.

1. We confirm the observation of Bürk (1965) that Neurospora crassa NADP-linked glutamate dehydrogenase normally exists in an inactive form below pH7.0 and in a fully active form above pH8.0 in either tris or orthophosphate buffer. At pH7.4 the enzyme is about half activated at 25 degrees . 2. The variety of the enzyme produced by the mutant am(2l) shows a similar behaviour except that the transition is shifted about one pH unit in the alkaline direction. 3. The am(2l) enzyme has previously been reported to be activated by brief warming to 30 degrees in phosphate buffer at pH8.0. The wild-type enzyme shows a similar effect at pH7.0. In tris buffer this effect is much less pronounced. 4. The am(2l) enzyme is extremely unstable at 47 degrees at pH7.0; its stability is somewhat greater at lower pH, and is markedly increased by increasing the pH in the range 7.0-8.7. The wild-type enzyme also shows an indication of a stability minimum at pH7.0, but a temperature of 60 degrees is needed for a measurable rate of inactivation. 5. The inactive form of the enzyme is much more subject to thermal irreversible denaturation than is the active form.

Glutamate Dehydrogenase↗