Ornithine and glutamate decarboxylases catalyse an oxidative deamination of their alpha-methyl substrates.
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.
Bertoldi
M
M
Dipartimento di Scienze Neurologiche e della Visione, Sezione di Chimica Biologica, Facoltà di Medicina e Chirurgia, Università degli Studi di Verona, Strada Le Grazie 8, 37134 Verona, Italy.
Carbone
V
V
Borri Voltattorni
C
C
D000641:Ammonia / Q000378:metabolism; D002384:Catalysis; D004926:Escherichia coli / Q000201:enzymology; D008401:Gas Chromatography-Mass Spectrometry; D005968:Glutamate Decarboxylase / Q000378:metabolism*; D007700:Kinetics; D007778:Lactobacillus / Q000201:enzymology; D007982:Levulinic Acids / Q000378:metabolism; D009955:Ornithine Decarboxylase / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption
D007982:Levulinic Acids; D000641:Ammonia; D005968:Glutamate Decarboxylase; D009955:Ornithine Decarboxylase; C032246:levulinic acid