Glycolytic enzymes in muscle of the Pacific dolphin: role of pyruvate kinase in aerobic-anaerobic transition during diving

Abstract

1.1. Glycolytic enzyme levels for skeletal muscle of the Pacific white striped dolphin (Lagenorhynchus obliquidens) were determined.2.2. Lactate dehydrogenase, aldolase and phosphoglucomutase levels are higher than in other mammalian skeletal muscles; pyruvate kinase is the only glycolytic enzyme in lower concentration in dolpin muscle.3.3. Pyruvate kinase from dolphin muscle displays an acid pH optimum, an unsual sensitivity to ATP product inhibition and an important regulation by fructose-1,6-dis- phosphate (FDP). The regulation by FDPinvolves both an increase in enzyme-substrate affinityas well as a reversal of ATP inhibition, and isthought to integrate pyruvate kinase activity with thatof phosphofructo-kinase during glycolytic activation in diving. The unsually potent ATP inhibitory control ofmuscle pyruvate kinase is thought to be involved in “turning off” pyruvate kinase at the end of diving, when carbohydrate is “s pared” in preference forother substrates, notably fatty acids.4.4. Fructose diphosphatase and glucose-6-phosphate dehydrogenase levels were found to correspond to those of other mammals suggesting little gluconeo- genic or pentose phosphate cycle activity in these muscles.