title: Biochemical and molecular characterization of alpha-ketoisovalerate decarboxylase, an enzyme involved in the formation of aldehydes from amino acids by Lactococcus lactis.
abstract: In this paper, we report for the first time on the identification, purification, and characterization of the alpha-ketoisovalerate decarboxylase from Lactococcus lactis, a novel enzyme responsible for the decarboxylation into aldehydes of alpha-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 alpha-keto acid decarboxylase included in the pyruvate decarboxylase group of enzymes. The active enzyme is a homo-tetramer that showed optimum activity at 45 degrees C and at pH 6.5 and exhibited an inhibition pattern typical for metal-dependant enzymes. In addition to Mg(2+), activity was observed in presence of other divalent cations such as Ca(2+), Co(2+) and Mn(2+). The enzyme showed the highest specific activity (80.7 Umg(-1)) for alpha-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.
authors.affiliation: Department of Dairy Science and Technology, Instituto del Frío (CSIC), Ciudad Universitaria, José Antonio Novais 10, 28040 Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: de la Plaza
authors.forename: Pilar
authors.initials: P
authors.lastname: Fernández de Palencia
authors.forename: Carmen
authors.initials: C
authors.lastname: Peláez
authors.forename: Teresa
authors.initials: T
authors.lastname: Requena
mesh_terms: D000447:Aldehydes / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism*; D002262:Carboxy-Lyases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D013294:Lactococcus lactis / Q000201:enzymology* / Q000235:genetics; D007930:Leucine / Q000096:biosynthesis; D016366:Open Reading Frames; D011773:Pyruvates / Q000378:metabolism; D014633:Valine / Q000096:biosynthesis
chemical_list: D000447:Aldehydes; D000596:Amino Acids; D011773:Pyruvates; D002262:Carboxy-Lyases; D007930:Leucine; D014633:Valine