Isolation and characterization of lactate dehydrogenase from white fin muscles of the skate Raja clavata

Lactate dehydrogenase (LDH) from white driving muscle of skate Raja clavata was purified by the differential precipitation of ammonium sulphate between 52 and 55% saturation. Only one protein band with the LDH activity was obtained by nondenaturing electrophoresis. The same result was obtained by the SDS-electrophoresis. The relative molecular weight calculated by this method in the presence of DS-Na was 34 kDa; Km was 29 +/- 7 and 71 +/- 16 microM for NAD.H and pyruvate, respectively. The reaction was maximally activated by 0.8-6.0 mM pyruvate and inhibited in the regions above this level. Dilution of LDH below concentration of 1 microgram/ml reduced the enzyme activity. The pH-optimum for the LDH activity ranged 7.0-8.0.