title: Kinetics of activation of L-lactate dehydrogenase from Streptococcus faecalis by fructose 1,6-bisphosphate and by metal ions.
abstract: The lactate dehydrogenase from Streptococcus faecalis is activated either by fructose 1,6-bisphosphate or by divalent cations such as Mn2+ or Co2+. With both types of activator, a lag is observed before attainment of the steady state rate of pyruvate reduction if the activator is added to the enzyme at the same time as the substrates. This lag can be largely abolished by preincubation of enzyme with activator before mixing with substrates. For fructose 1,6-bisphosphate (Fru(1,6)P2) as the activator, the rate constant for the lag phase showed a linear dependence on activator concentration but was independent of enzyme concentration. This suggests that binding of fructose 1,6-bisphosphate induces a conformational change in the enzyme which leads to increased activity, without association of enzyme subunits or dimers. With Co2+ as activator, the rate constant for the lag phase showed a hyperbolic dependence on Co2+ concentration and was also dependent on enzyme concentration. This suggests that activation by Co2+, in contrast to that by Fru(1,6)P2, involves association of enzyme dimers, followed by ligand binding.
mesh_terms: D003035:Cobalt / Q000494:pharmacology*; D013293:Enterococcus faecalis / Q000201:enzymology*; D004789:Enzyme Activation; D005635:Fructosediphosphates / Q000494:pharmacology*; D006598:Hexosediphosphates / Q000494:pharmacology*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D008345:Manganese / Q000494:pharmacology*
chemical_list: D005635:Fructosediphosphates; D006598:Hexosediphosphates; D003035:Cobalt; D008345:Manganese; D007770:L-Lactate Dehydrogenase