Metabolic priorities during starvation: enzyme sparing in liver and white muscle of Atlantic cod, Gadus morhua L.

Atlantic cod, Gadus morhua, respond to starvation first by mobilising hepatic lipids, then muscle and hepatic glycogen and finally muscle proteins. The dual role of proteins as functional elements and energetic reserves should lead to a temporal hierarchy of mobilisation where the nature of a function dictates its conservation during starvation. We examined (1) whether lysosomal and anti-oxidant enzymes in liver and white muscle are spared during prolonged starvation, (2) whether the responses of these enzymes in muscle vary longitudinally. Hepatic contents of lysosomal proteases decreased with starvation, whereas those of catalase (CAT) increased and lysosomal enzymes of carbohydrate metabolism and glutathione S-transferase (GST) did not change. In white muscle, starvation decreased the specific activity of lysosomal enzymes of carbohydrate degradation and doubled that of cathepsin D (CaD). The activity of anti-oxidant enzymes and acid phosphatase in muscle was unchanged with starvation. In white muscle neither lysosomal enzymes nor anti-oxidant enzymes varied significantly with sampling position. In cod muscle, antioxidant enzymes, CaD and acid phosphatase are spared during a period of starvation that decreases lysosomal enzymes of carbohydrate metabolism and decreases glycolytic enzyme activities. In cod liver, the anti-oxidant enzymes, CAT and GST, were also spared during starvation.