title: Intracellular pH and the role of D-lactate dehydrogenase in the production of metabolic end products by Leuconostoc lactis.
abstract: The kinetics of lactate dehydrogenase from Leuconostoc lactis NCW1 were studied. The pH optimum for the enzyme depended on the concentration of pyruvate used in the assay and the enzyme displayed an ordered mechanism with respect to substrate binding. The Km for pyruvate and NADH and the Vmax of the enzyme decreased 20-, 30- and 6-fold respectively as the pH decreased from 8.0 to 5.0. No activators were found and none of the intermediates of the phosphoketolase pathway tested inhibited the enzyme. ATP, ADP, GTP and NAD+ were inhibitory. The intracellular volume (Vol(in)) and intracellular pH (pH(in)) decreased as the extracellular pH (pH(ex)) decreased. Co-metabolism of citrate and glucose affected the Vol(in) but did not affect the pH(in), which decreased by 0.6 units per unit change in pH(ex); at pH 7.0, the pH(in) and pH(ex) were equal. The results suggest that pH(in) may play a role in determining the production of diacetyl and acetoin at low pH by Leuconostoc.
authors.affiliation: National Dairy Products Research Centre, Moorepark, Fermoy, Co. Cork, Irish Republic.
authors.forename: R J
authors.initials: RJ
authors.lastname: FitzGerald
authors.forename: S
authors.initials: S
authors.lastname: Doonan
authors.forename: L L
authors.initials: LL
authors.lastname: McKay
authors.forename: T M
authors.initials: TM
authors.lastname: Cogan
mesh_terms: D000244:Adenosine Diphosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D004789:Enzyme Activation; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007934:Leuconostoc / Q000201:enzymology*; D009243:NAD / Q000378:metabolism / Q000494:pharmacology; D011773:Pyruvates / Q000378:metabolism; D019289:Pyruvic Acid
chemical_list: D011773:Pyruvates; D009243:NAD; D000244:Adenosine Diphosphate; D019289:Pyruvic Acid; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D007770:L-Lactate Dehydrogenase