Isolation of NAD-dependent and NAD-independent lactate dehydrogenases from extracts of butyribacterium rettgeri

1.1. Cell extracts of lactate-grown Butyribacterium rettgeri catalyze the reduction of pyruvate to lactate with NADH2 and also catalyze the reduction of ferricyanide or DCIP by lactate without the participation of NAD coenzymes.2.2. Both types of lactate dehydrogenase are “soluble”, i.e., both activities are quantitatively recovered in the supernatant fluid after centrifugation of cell-free extracts at 144 000 × g for 90 min.3.3. The two types of lactate dehydrogenase activity have been separated from one another by a combination of (NH4)2SO4 fractionations and DEAE-cellulose chromatography.4.4. The isolated NAD-independent enzyme activity is extremely labile to storage and is stimulated by relatively high concentrations of certain inorganic salts. In contrast, the isolated NAD-linked enzyme activity is stable to storage and is unaffected by inorganic salts.5.5. NAD-independent enzyme preparations, isolated by DEAE-cellulose chromatography, utilize either d(−)- or l(+)-lactate as a substrate for dye reduction. These preparations have been shown to contain two stereospecific lactate dehydrogenases.6.6. Other properties of the NAD-independent enzyme system are given and its role in lactate degradation is discussed.