Effects of Starvation on the Activities and Localization of Glycolytic Enzymes in the White Muscle of the Barred Sand Bass Paralabrax nebulifer

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Abstract
During starvation the metabolism of"nonfatty" fish, i.e., fish with limited reserves of lipid, is supported to a significant extent by the degradation of proteins in white muscle. We have investigated the effects of starvation on selected glycolytic enzymes and actin in white muscle of the barred sand bass Paralabrax nebuhlifer. The concentration of actin remains stable during 4 wk of starvation, but the activities of the glycolytic enzymes phosphofructokinase (PFK), aldolase (ALD), glyceraldehyde-3phosphate dehydrogenase (GAPDH), and pyruvate kinase (PK) all decrease. Using a new detergent extraction technique for separating the soluble and myofibrillar proteins of muscle, we show that the intracellular localization of these glycolytic enzymes shifts during starvation. A decreased percentage of the total enzymatic activity is found associated with the myofibrils in starved fish. PFK, an important regulatory enzyme in glycolysis, shows the most striking shift in compartmentation. Refeeding fish starved for 21 days led to a near-complete recovery of enzymatic activity within 24 h. However, only PFK regained the myofibrillar association noted in fed fish. The changes in the activities and intracellular localizations of these enzymes are discussed in terms of the energetics of starvation, the selective degradation of proteins during starvation, and the physiological significance of glycolytic enzyme distribution between soluble and myofibrillar compartments in muscle.