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Biomedical subjects

M J Hynes

Publications and source records attributed to M J Hynes.

At least 91 records · Page 5Linked to original sources
PubMed1980

A mutation, adjacent to gene amdS, defining the site of action of positive-control gene amdR in Aspergillus nidulans.

In Aspergillus nidulans the acetamidase enzyme is inducible by omega-amino acids, sources of acetyl-coenzyme A, and benzoate. The amdR (or intA) gene is a positive-control gene involved in omega-amino acid induction only. A cis-acting mutation amdI93 located in a complex controlling region adjacent to the acetamidase structural gene was found to abolish induction by omega-amino acids but not induction by other sources of induction. As predicted, this mutation was epistatic to constitutive amdR alleles but did not affect the expression of mutations in other regulatory genes.

Acetamides↗
PubMed1979

Fine-structure mapping of the acetamidase structural gene and its controlling region in Aspergillus nidulans.

A large number of amdS mutants altered in acetamide utilization have been used to construct a fine-structure map of the amdS locus. The mutagen diepoxyoctane generated most of the deletion strains used for mapping. A minimum of 14 sites within the amdS gene were found. Biochemical analysis of amdS mutants defined the extent of the probable coding region. A new mutant, amd-205, which did not produce detectable inactive gene product, was found to be inseparable by recombination from the "up-promoter" mutation amdI18 and was located outside of the apparent amdS coding region. The cis-dominant mutation, amdI9, was also located at this end of the gene. This work, therefore, provides evidence for the separation of a eukaryotic gene into controlling and structural regions.

Acetamides↗
PubMed1978

An "up-promotor" mutation affecting the acetamidase of Aspergillus nidulans.

A derivative of an areA200 strain of Aspergillus nidulans selected for strong growth on acetamide as the sole nitrogen source was found to have a mutation, amd-18, closely linked to amdS, the acetamidase structural gene. This mutation results in 2--3 fold higher acetamidase activities than wildtype strains in uninduced as well as induced cultures. The effects of the amd-18 mutation are superimposed on the effects of other regulatory mutations affecting the acetamidase. The amd-18 mutation is cis-dominant with respect to the amdS gene. Immunological and gel electrophoresis studies have shown that amd-18 strains produce higher levels of acetamidase protein. A previously described cis-dominant mutation, amdI9, also causes elevated levels of acetamidase protein. The amd-18 mutation may affect a promoter site for the amdS gene allowing an increased frequency of transcription.

Acetamides↗
PubMed1978

Multiple independent control mechanisms affecting the acetamidase of Aspergillus nidulans.

The acetamidase of Aspergillus nidulans is induced by sources of acetyl CoA, benzoate and benzamide and by beta-alanine and other omega-amino acids. The effects of these groups of inducers are appromimately additive. The cis-acting control site mutant, amdI9, affects induction by sources of acetyl-CoA specifically. Lesions in the amdR and gatA genes affect induction by omega-amino acids specifically. Mutations in the amdA gene can lead to elevated acetamidase levels which still respond to the various inducers. The induction controls act independently of repression control by nitrogen metabolites and are not altered by the areA102 mutation. The properties of double mutants with lesions affecting the different control mechanisms also indicate their independence of each other. It is suggested that the acetamidase is subject to complex control by multiple regulatory circuits and that functionally independent control sites adjacent to the structural gene occur.

Acetamides↗
PubMed1978

Stopped-flow spectrophotometric studies on the reaction of turkey liver xanthine dehydrogenase with reducing substrates.

The kinetics of reduction of turkey liver xanthine dehydrogenase by substrates were investigated by stopped-flow spectrophotometry. The results may be explained in terms of the known redox potentials of the various centres in the enzyme [Barber, Bray, Cammack & Coughlan (1977) Biochem. J. 163, 279-289]. They are, morover, consistent with the scheme [Olson, Ballou, Palmer & Massey (1974) J. Biol. Chem. 249, 4363-4382] in which reduction occurs in three consecutive steps, one molecule of substrate reacting with the active site at each step. First-order rate constants believed to correspond respectively to the combined first and second steps and to the third step in the reduction by excess of xanthine and of NADH were determined. The rates of reaction with these substrates in the combined first and second steps are independent of the degree of enzyme functionality.

Animals↗
PubMed1977

Increased and decreased sensitivity to carbon catabolite repression of enzymes of acetate metabolism in mutants of Aspergillus nidulans.

The creA204, creB15 and creC27 mutations have been shown to cause carbon catabolite derepression of acetly CoA synthase and isocitrate lyase in Aspergillus nidulans. A recessive mutation, cre-34, which is linked to the creC gene, results in these enzymes being more sensitive than cre or wildtype strains to catabolite repression. The acetamidase levels of strains containing cre mutations have been investigated and provide support for the hypothesis that an acetate metabolite, rather than acetamide, induces this enzyme.

Acetate-CoA Ligase↗
PubMed1977

Pleiotropic mutants of Aspergillus nidulans altered in carbon metabolism.

Mutants altered in carbon catabolite regulation have been isolated by selecting for mutants of the areA217 strain capable of using acetamide as the sole nitrogen source in the presence of sucrose. In addition to creA mutants described previously be Arst and Cove, strains with mutations in two new genes, creB and cre C, have been found. The creB and creC mutants grow poorly on some sole carbon sources and have low levels of some enzymes of carbon catabolism e.g. beta-galactosidase and D-quinate dehydrogenase. The creB and creC mutants are hypersensitive to fluoroacetate, fluoroacetamide and allyl alcohol in the presence of glucose or sucrose but not glycerol; and the enzymes, acetamidase and alcohol dehydrogenase, are less sensitive to carbon catabolite repression than the wild-type strain. Extracellular protease and alpha-glucosidase enzyme activities are elevated in creB and creC mutants, while L-proline and L-glutamate uptake capacities are lower in both the presence and absence of glucose. Interactions between creA, B and C mutations have been investigated in double mutants, and the dominance properties of creB and creC mutants determined. The results indicate that the creB and creC genes may have a regulatory role in the control of carbon catabolism.

Acetamides↗
PubMed1977

Induction of the acetamidase of Aspergillus nidulans by acetate metabolism.

Growth tests and enzyme determinations strongly suggest that the acetamidase of Aspergillus nidulans is induced by a product of acetate metabolism rather than the substrate, acetamide. The cis-dominant mutation, amdI9, which is closely linked to amdS, the structural gene for the acetamidase, results in greatly increased sensitivity to induction by acetate metabolism. Propionate, L-threonine, and ethanol also result in acetamidase induction. Mutations in the facA, facB, and facC genes, which lead to low levels of acetyl-coenzyme A synthase, are epistatic to the amdI9 mutation for strong growth on acetamide medium and abolish acetamide and propionamide induction of the acetamidase and isocitrate lyase enzymes. Acetate, L-threonine, and ethanol, however, can induce these enzymes in strains containing facA and facC lesions but not in strains containing a facB lesion. The evidence suggests that acetamidase and isocitrate lyase may be induced by a similar mechanism.

Acetamides↗
PubMed1975

Studies on the role of the areA gene in the regulation of nitrogen catabolism in Aspergillus nidulans.

Mutants of Apergillus nidulans with lesions in a gene, areA (formerly called amdT), have been isolated by a variety of different selection methods. The areA mutants show a range of pleiotropic growth responses to a number of compounds as sole nitrogen sources, but are normal in utilization of carbon sources. The levels of two amidase enzymes as well as urease have been investigated in the mutants and have been shown to be affected by this gene. Most of the areA mutants have much lower amidase-specific activities when grown in ammonium-containing medium, compared with mycelium incubated in medium lacking a nitrogen source. Some of the areA mutants do not show derepression of urease upon relief of ammonium repression. The dominance relationships of areA alleles have been investigated in heterozygous diploids, and these studies lend support to the proposal that areA codes for a positively acting regulatory product. One of the new areA alleles is partially dominant to areA+ and areA102. This may be a result of negative complementation or indicate that areA has an additional negative regulatory function. Investigation of various amdR; areA double mutants has led to the conclusion that amdR and areA participate in independent regulatory circuits in the control of acetamide utilization. Studies on an amdRc; areA double mutant indicate that areA is involved in derepression of acetamidase upon relief of ammonium repression.

Acetamides↗
PubMed1975

Amide utilization in Aspergillus nidulans: evidence for a third amidase enzyme.

A mutation in a gene designated gmdA has been found to lead to loss of ability of Aspergillus nidulans to use benzamide, phenylacetamide and several other amides as sole nitrogen sources for growth. The gmdA1 lesion results in low levels of an enzyme, called the general amidase, which has acitivity for a wide range of amide substrates. This enzyme is reressed by certain nitrogen-containing metabolites, including ammonium, but is probably not regulated by induction or by carbon catabolite repression. Evidence is presented for the general amidase being distinct from the previously characterized acetamidase and formamidase enzymes. The data also indicate that there is a fourth amidase capable of the hydrolysis of valeramide and hexanamide.

Acetamides↗
PubMed1975

Enzymology and genetic regulation of a cyclic nucleotide-binding phosphodiesterase-phosphomonoesterase from Aspergillus nidulans.

A cyclic nucleotide-binding phosphohydrolase that possesses both a phosphomonoesterase and a phosphodiesterase catalytic function has been partially purified from Aspergillus nidulans. The enzyme hydrolyzes both p-nitrophenylphosphate and bis-(p-nitrophenyl)-phosphate. o'-Nucleoside monophosphates are the best physiological phosphomonesterase substrates but 5'- and 2'-nucleoside monophosphates are also hydrolyzed. The enzyme catalyzes the hydrolysis of adenosine 5'-triphosphate, adenosine 5'-diphosphate, and 2',3'- and 3'5'-cyclic nucleotides, but not of ribonucleic acid, deoxyribonucleic acid, or nicotinamide adenine dinucleotide. The enzyme has acid pH optima and is not activated by divalent cations. Nucleosides and nucleotides inhibit the enzyme. Cyclic nucleotides are competitive inhibitors of the phosphodiesterase-phosphomonoesterase. The enzyme can occur extracellularly. The phosphodiesterase-phosphomonoesterase is present at high levels in nitrogen-starved mycelium, and it is strongly repressed during growth in media containing ammonium or glutamine and weakly repressed during growth in glutamate-containing medium. Experiments with various area mutants show that this regulatory gene is involved in the control of the enzyme. No evidence for regulation of the enzyme by carbon or phosphorus starvation has been found.

Aspergillus nidulans↗