[The effect of temperature acclimation on NADP-dependent dehydrogenase activity in the carp liver and various mechanisms of its regulation].

Acclimation of carp both to the temperature fall (from 20 to 5 degrees C) and rise (from 20 to 30 degrees C) induces an increase in activity of cytoplasmic liver NADPH-generating enzymes--glucose-6-phosphate dehydrogenase (G6PDG) and malic-enzyme (ME) 6-phosphogluconate dehydrogenase (6PGDG) and NADP-isocitrate dehydrogenase (NADP-IDG) activities are unchanged. Actinomycin D does not prevent cold activation of G6PDG but blocks activation of ME. "Warm" G6PDG has minimal Km value for glucose-6-phosphate and "warm" ME has minimal Km value for glucose-6-phosphate and "warm" ME has minimal Km value for malate at 25 degrees C "Cold" G6PDG and ME have the warmest Km values at 5 degrees C. Isozyme composition of cytoplasmic G6PDG (2 bands with Rf 0.16 and 0.20) does not change within the limits of 5-30 degrees C. The prolactin action on G6PDG and ME is similar to the effect of cold acclimation (activity increases Km value decreases, isozyme pattern (for G6PDG) remains unchanged). It is supposed that activation of G6PDG and ME during cold adaptation may be a result of the prolactin action on substrate-binding ability without changes in the enzyme biosynthesis and isozyme pattern.