Cytoplasmic sources of NADPH for fat synthesis in rainbow trout liver: Effect of thermal acclimation on enzyme activities

Abstract

1. 1. Activity levels of the enzymes NADP malate dehydrogenase, NADP isocitrate dehydrogenase, Glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, NAD malate dehydrogenase and ATP citrate lyase, have been determined in cytoplasmic preparations of liver from warm and cold acclimated rainbow trout. 2. 2. The activity levels of the four NADP dehydrogenases are similar and do not change significantly following cold acclimation, suggesting that regulation of NADPH production is achieved by mechanisms other than alterations in the steady state levels of these enzymes. 3. 3. The absence of ATP citrate lyase activity may indicate that the levels are too low to detect by the assay method and the enzyme may be rate limiting in the pathway, or that a pyruvate-malate cycle is inoperative in this tissue.