PMID:10477260
| Citation |
Bertoldi, M, Carbone, V and Borri Voltattorni, C (1999) Ornithine and glutamate decarboxylases catalyse an oxidative deamination of their alpha-methyl substrates. Biochem. J. 342 Pt 3:509-12 |
|---|---|
| Abstract |
Ornithine decarboxylase (ODC) from Lactobacillus 30a catalyses the cleavage of alpha-methylornithine into ammonia and 2-methyl-1-pyrroline; glutamate decarboxylase (GAD) from Escherichia coli catalyses the cleavage of alpha-methylglutamate into ammonia and laevulinic acid. In our analyses, 2-methyl-1-pyrroline and laevulinic acid were identified by HPLC and mass spectroscopic analysis, and ammonia was identified by means of glutamate dehydrogenase. Molecular oxygen was consumed during these reactions in a 1:2 molar ratio with respect to the products. The catalytic efficiencies (k(cat)/K(m)) of the reactions catalysed by ODC and GAD were determined as 12500 and 9163 M(-1).min(-1) respectively. When the reactions were performed under anaerobic conditions, no ammonia, 2-methyl-1-pyrroline or laevulinic acid was produced to a significant extent. The formation of ammonia and O(2) consumption (in a 1:2 molar ratio with respect to ammonia) were also detected during the reaction of ODC and GAD with putrescine and gamma-aminobutyrate respectively. Taken together, these findings clearly indicate that ODC and GAD catalyse an oxidative deamination of their decarboxylation products, a reaction similar to that catalysed by dopa decarboxylase (DDC) with alpha-methyldopa [Bertoldi, Dominici, Moore, Maras and Borri Voltattorni (1998) Biochemistry 37, 6552-6561]. Furthermore, this reaction was accompanied by a decarboxylation-dependent transamination occurring for GAD, DDC and ODC with a frequency of approx. 0.24%, 1% and 9% respectively compared with that of oxidative deamination. |
| Links | |
| Keywords |
Ammonia/metabolism; Catalysis; Escherichia coli/enzymology; Gas Chromatography-Mass Spectrometry; Glutamate Decarboxylase/metabolism; Kinetics; Lactobacillus/enzymology; Levulinic Acids/metabolism; Ornithine Decarboxylase/metabolism; Oxidation-Reduction; Oxygen Consumption |
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