Sites and patterns of protein and amino acid utilization during the spawning migration of salmon

Abstract

Some aspects of the biochemistry of sockeye salmon (Oncorhynchns nerka) were investigated during spawning migration in the Fraser River, B.C. Studies included measurements of the activities of metabolic enzymes, protein content, and free amino acid concentrations in various tissues. In white muscle, soluble and insoluble protein decreased by 70% during migration and the activities of most of the enzymes studied showed a similar pattern. In contrast, the activities of cathepsin D (EC 3.4.23.5) and carboxypeptidase A (EC 3.4.12A.1) increased considerably, whereas the activities of alanine aminotransferase (EC 2.6.1.2) and malic enzyme (EC 1.1.1.40) were unchanged during migration. In red muscle and heart there was little change in either protein levels or enzyme activities, with the exception of glucose-6-phosphate dehydrogenase (EC 1.1.1.4), which increased threefold to sixfold. In liver, the activities of metabolic enzymes and the levels of soluble protein decreased, whereas proteolytic enzyme activities increased slightly during migration.It is concluded that white muscle is the primary source of the amino acids utilized during migration. A model is proposed to account for the fate of the amino acids released by proteolysis in white muscle. It is suggested that most of the amino acids are collected as alanine and transported to other tissues in this form.