Abstract
The glutamine synthetase of Neurospora crassa, either purified or in cell extracts, was inactivated by ascorbate plus FeCl3 and by H2O2 plus FeSO4. The inactivation reaction was oxygen dependent, inhibited by MnCl2 and EDTA, and stimulated in cell extracts by sodium azide. This inactivation could also be brought about by adding NADPH to the cell extract. The alpha and beta polypeptides of the active glutamine synthetase were modified by these inactivating reactions, giving rise to two novel acidic polypeptides. These modifications were observed with the purified enzyme, with cell extracts, and under in vivo conditions in which glutamine synthetase is degraded. The modified glutamine synthetase was more susceptible to endogenous phenylmethylsulfonyl fluoride-insensitive proteolytic activity, which was inhibited by MnCl2 and stimulated by EDTA. The possible physiological relevance of enzyme oxidation is discussed.
Highlights
Our research on the regulation of nitrogen metabolism during the formation of Neurospora crassa aerial mycelia suggested that in the mycelium forming the aerial hyphae
Manganese and EDTA suppressed inactivation in the presence of air. These results suggested that the glutamine synthetase (GS) of N. crassa
In this paper we have studied the oxidative inactivation of GS in N. crassa
Summary
JESUS AGUIRRE AND WILHELM HANSBERG* Centro de Investigacion sobre Fijacion de Nitr6geno, Universidad Nacional Aut6noma de Mexico, Cuernavaca, Morelos, Mexico. The inactivation reaction was oxygen dependent, inhibited by MnCl2 and EDTA, and stimulated in cell extracts by sodium azide. The ax and polypeptides of the active glutamine synthetase were modified by these inactivating reactions, giving rise to two novel acidic polypeptides. These modifications were observed with the purified enzyme, with cell extracts, and under in vivo conditions in which glutamine synthetase is degraded. The modified glutamine synthetase was more susceptible to endogenous phenylmethylsulfonyl fluoride-insensitive proteolytic activity, which was inhibited by MnCl2 and stimulated by EDTA. We report that oxidation of N. crassa GS ot and ,3 polypeptides inactivated the enzyme, giving rise to two novel acidic polypeptides which were more susceptible to proteolysis than the unmodified ones. The data suggest that the modification reaction can occur in vivo and is related to the physiological conditions of the fungus
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