Enzyme activity levels underestimate lactate production rates in cod (Gadus morhua) gas gland

Abstract

Maximal in vitro activities of hexokinase, phosphofructokinase, pyruvate kinase, lactate dehydrogenase, β-hydroxyacyl-CoA dehydrogenase, citrate synthase, malate dehydrogenase, and cytochrome oxidase were assessed in cod (Gadus morhua) gas gland. The metabolic profile predicts a substantial anaerobic relative to aerobic metabolism. The effect of catecholamines, acetylcholine, and low pH on in vitro rates of lactate production by gas gland was assessed. Adrenaline and acetylcholine both increased the rate of lactate production even under aerobic incubation conditions. However, the rates of lactate production were well below the capacity suggested by the enzyme levels. It is suggested that the tissue has an abundance of enzymes that operate at submaximal rates.