title: Characterization of the L-lactate dehydrogenase from Aggregatibacter actinomycetemcomitans.
abstract: Aggregatibacter actinomycetemcomitans is a Gram-negative opportunistic pathogen and the proposed causative agent of localized aggressive periodontitis. A. actinomycetemcomitans is found exclusively in the mammalian oral cavity in the space between the gums and the teeth known as the gingival crevice. Many bacterial species reside in this environment where competition for carbon is high. A. actinomycetemcomitans utilizes a unique carbon resource partitioning system whereby the presence of L-lactate inhibits uptake of glucose, thus allowing preferential catabolism of L-lactate. Although the mechanism for this process is not fully elucidated, we previously demonstrated that high levels of intracellular pyruvate are critical for L-lactate preference. As the first step in L-lactate catabolism is conversion of L-lactate to pyruvate by lactate dehydrogenase, we proposed a model in which the A. actinomycetemcomitans L-lactate dehydrogenase, unlike homologous enzymes, is not feedback inhibited by pyruvate. This lack of feedback inhibition allows intracellular pyruvate to rise to levels sufficient to inhibit glucose uptake in other bacteria. In the present study, the A. actinomycetemcomitans L-lactate dehydrogenase was purified and shown to convert L-lactate, but not D-lactate, to pyruvate with a K(m) of approximately 150 microM. Inhibition studies reveal that pyruvate is a poor inhibitor of L-lactate dehydrogenase activity, providing mechanistic insight into L-lactate preference in A. actinomycetemcomitans.
authors.affiliation: Section of Molecular Genetics and Microbiology, The University of Texas at Austin, Austin, Texas, United States of America.
authors.forename: Stacie A
authors.initials: SA
authors.lastname: Brown
authors.forename: Marvin
authors.initials: M
authors.lastname: Whiteley
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry; D001692:Biological Transport; D002244:Carbon / Q000737:chemistry; D015971:Gene Expression Regulation, Enzymologic; D005947:Glucose / Q000378:metabolism; D006090:Gram-Negative Bacteria / Q000201:enzymology*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000737:chemistry* / Q000235:genetics; D019344:Lactic Acid / Q000737:chemistry; D008954:Models, Biological; D009243:NAD / Q000737:chemistry; D017434:Protein Structure, Tertiary; D019289:Pyruvic Acid / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D009243:NAD; D019344:Lactic Acid; D002244:Carbon; D019289:Pyruvic Acid; D007770:L-Lactate Dehydrogenase; D005947:Glucose