Ornithine and glutamate decarboxylases catalyse an oxidative deamination of their alpha-methyl substrates

Biochem J. 1999 Sep 15;342 Pt 3(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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 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

Substances

  • Levulinic Acids
  • Ammonia
  • Glutamate Decarboxylase
  • Ornithine Decarboxylase
  • levulinic acid