RESUMO
In Aspergillus nidulans there are three NAD(+)-dependent alcohol dehydrogenases (ADHs) that are capable of utilizing ethanol as a substrate. ADHI is the physiological enzyme of ethanol catabolism and ADHIII is induced under conditions of anaerobiosis. The physiological role of ADHII (structural gene alcB) is unknown. We have measured beta-galactosidase in a transformant with an alcB::lacZ fusion and have shown that alcB is maximally expressed under conditions of carbon starvation. The behavior of the alcB::lacZ transformant suggests a hierarchy of repressing carbon sources characteristic of repression by the general carbon catabolite repressor protein, CreA, but in a creA(d)30 background the transformant shows only partial derepression of beta-galactosidase on 1% glucose compared to the creA+ strain. Our results suggest that, in addition to carbon catabolite repression acting via CreA, a CreA-independent mechanism is involved in induction of alcB on carbon starvation.
Assuntos
Álcool Desidrogenase/biossíntese , Aspergillus nidulans/enzimologia , Carbono/metabolismo , Proteínas Fúngicas/biossíntese , Álcool Desidrogenase/genética , Aspergillus nidulans/metabolismo , Proteínas de Ligação a DNA/metabolismo , Indução Enzimática , Repressão Enzimática , Etanol/metabolismo , Proteínas Fúngicas/metabolismo , Regulação Fúngica da Expressão Gênica , Mutação , Proteínas Repressoras/metabolismoRESUMO
In Aspergillus nidulans three alcohol dehydrogenases (ADHs) have been described. ADHI is induced by ethanol and is the physiological enzyme of ethanol utilization, ADHII has not been attributed a function but is repressed by ethanol. The ALCR regulatory protein acts positively to induce ADHI, and negatively in its control of ADHII. ADHIII is specifically induced by anaerobic stress. We have characterized the substrate specificity of these three enzymes by looking at their staining profile on polyacrylamide gels with a range of alcohols. In addition to these enzymes we have observed six other NAD(+)-dependent ADHs, two of which, propan-2-ol dehydrogenase and pentan-2-ol dehydrogenase, share similar control with ADHII. The inducibility of these enzymes with some alcohols has also been investigated. The profile of ADHs with NADP+ as an electron acceptor is also reported.
Assuntos
Álcool Desidrogenase/metabolismo , Álcoois/metabolismo , Aspergillus nidulans/enzimologia , Proteínas Fúngicas/metabolismo , NAD/metabolismo , Álcool Desidrogenase/classificação , Proteínas de Ligação a DNA/fisiologia , Indução Enzimática , Proteínas Fúngicas/fisiologia , Regulação Fúngica da Expressão Gênica , NADP/metabolismo , Especificidade por SubstratoRESUMO
In Aspergillus nidulans there is an NADP(+)-dependent glycerol dehydrogenase that is specifically induced on transfer to D-galacturonate medium. In contrast to the previously characterised constitutive NADP(+)-dependent glycerol dehydrogenase it has a much broader substrate specificity, having activity as an ethanol dehydrogenase, and is subject to carbon-catabolite repression. In addition to the two NADP(+)-dependent glycerol dehydrogenases, alcohol dehydrogenase I and II are also present on transfer to D-galacturonate medium, and have weak activity as glycerol dehydrogenases.
