Biochemical and molecular characterization of α-ketoisovalerate decarboxylase, an enzyme involved in the formation of aldehydes from amino acids byLactococcus lactis

In this paper, we report for the first time on the identification, purification, and characterization of the α-ketoisovalerate decarboxylase from Lactococcus lactis, a novel enzyme responsible for the decarboxylation into aldehydes of α-keto acids derived from amino acid transamination. The kivd gene consisted of a 1647 bp open reading frame encoding a putative peptide of 61 kDa. Analysis of the deduced amino acid sequence indicated that the enzyme is a non-oxidative thiamin diphosphate (ThDP)-dependent α-keto acid decarboxylase included in the pyruvate decarboxylase group of enzymes. The active enzyme is a homo-tetramer that showed optimum activity at 45 °C and at pH 6.5 and exhibited an inhibition pattern typical for metal-dependant enzymes. In addition to Mg2+, activity was observed in presence of other divalent cations such as Ca2+, Co2+ and Mn2+. The enzyme showed the highest specific activity (80.7 U mg−1) for α-ketoisovalerate, an intermediate metabolite in valine and leucine biosynthesis. On the other side, decarboxylation of indole-3-pyruvate and pyruvate only could be detected by a 100-fold increase in the enzyme concentration present in the reaction.