Alpha-glycerophosphate dehydrogenase: Its role in the control of the cytoplasmic arm of the alpha-glycerophosphate cycle in squid mantle

Abstract

1.1. Squid muscle α-glycerophosphate dehydrogenase occurs in very high specific activity and single electrophoretic form with a broad pH optimum in the neutral range.2.2. Arrhenius plots are linear between 0° and 20°C with a Q10 of about 2·5. The plots show a distinct break at about 20°C with a reduced Q10 between 20° and 30°C. Because this complex behaviour is expressed with a highly purified enzyme preparation, it is indicative of temperature-dependent conformational transitions and a highly labile enzyme structure.3.3. The enzyme is inhibited by pressure; at 10°C, 50% inhibition is reached at 2700 psi.4.4. Kinetic evidence suggests that in vivo the enzyme serves as a unidirectional cayalyst promoting α-glycerophosphate formation while simultaneously designed to prevent its oxidation.5.5. The enzyme is under inhibitory control by ATP and NAD, the respective KI values being 0·7 mM and 2·0 mM.