L-LACTATE SPECIFIC, DIMERIC LACTATE-DEHYDROGENASE FROM THE MANTLE MUSCLE OF THE SQUID, LOLIGO-VULGARIS - PURIFICATION AND CATALYTIC PROPERTIES

1. 1. LDH from the mantle muscle of the squid, Loligo vulgaris, was purified to homogeneity by gel filtration on Sephadex G-150, affinity chromatography on Blue Sephadex G-200 and ion-exchange chromatography on DEAE-Sephadex A-50. 2. 2. The enzyme was found to be specific for l-lactate and the molecular weight, as judged by gel filtration, was calculated to be 70,000 daltons. A dimeric subunit organisation is suggested with subunits of 36,000 daltons (obtained from SDS electrophoresis). 3. 3. Michaelis constants of the enzyme are 0.69, 0.036 and 17 mM for pyruvate, NADH and l-lactate respectively. NAD+ showed a non-Michaelis-Menten behaviour. 4. 4. Although Loligo l-LDH kinetically resembles muscle-type mammalian LDH, the enzyme was inhibited by increasing concentrations of pyruvate, a characteristic of H-type mammalian LDH. 5. 5. The absence of ODH in the mantle muscle of this particular specimen of Loligo is discussed and two possibilities offered. © 1979.