Abstract
Three homofermentative ( Lactobacillus plantarum B38, L. plantarum B33, Pediococcus pentosaceus B30) and three heterofermentative ( Leuconostoc mesenteroides 39, L. oenos B70, Lactobacillus brevis ) lactic acid bacteria were examined for the presence or absence of nicotinamide adenine dinucleotide (NAD)-dependent and NAD-independent d - and l -lactate dehydrogenases. Two of the six strains investigated, P. pentosaceus and L. oenos , did not exhibit an NAD-independent enzyme activity capable of reducing dichlorophenol indophenol. The p H optima of the lactic dehydrogenases were determined. The NAD-dependent enzymes from homofermentative strains exhibited optima at p H 7.8 to 8.8, whereas values from 9.0 to 10.0 were noted for these enzymes from heterofermentative organisms. The optima for the NAD-independent enzymes were between 5.8 and 6.6. The apparent Michaelis-Menten constants determined for both NAD and the substrates demonstrated the existence of a greater affinity for d - than l -lactic acid. A comparison of the specific NAD-dependent and NAD-independent lactate dehydrogenase activities revealed a direct correlation of the d/l ratios of these activities with the type of lactic acid produced during the growth of the organism.