Kinetic parameters of lactate dehydrogenases of some rumen bacterial species, the anaerobic ciliate Isotricha prostoma and mixed rumen microorganisms.

A number of kinetic parameters of the lactate dehydrogenases of three rumen bacterial species (Peptostreptococcus productus, Propionibacterium acnes and Actinomyces viscosus), the rumen ciliate Isotricha prostoma and mixed rumen microorganisms (MRM) with respect to NADH, pyruvate, fructose-1,6-diphosphate (FDP) as well as the effects of several nucleotide phosphates were studied. Partially purified LDH of Peptostr. productus had the same kinetic parameters as in crude cell free extracts. Values for Km, determined by Michaelis-Menten kinetics with pyruvate as the substrate, were in the same range for all lactate dehydrogenases. After feeding a cow, changes in the apparent Km and Vmax values for NADH of the total LDH activity in MRM were followed. It is suggested that of the factors studied the ratio NADH/NAD(H) and ATP are the most important regulatory factors for the lactate dehydrogenases of mixed rumen microorganisms.