Free Amino Acid Composition of the Skeletal Muscle of Migratory Fish

It was confirmed that, in the usual cation-exchange column chromatographic method widely used for separating basic amino acids, anserine and lysine overlap and histidine emerges from the column together with carnosine and balenine. These facts strongly sug-gest that the reported values for free histidine and lysine in the muscle of fish-especially of dark-fleshed fish, such as tuna, skipjack and yellowtail-should be reviewed, and that the modified methods proposed by us should be employed for determining basic amino acids and imidazole dipeptides. The distribution of free amino acids as well as imidazole dipeptides and creatine (+creatinine) in skeletal muscle was examined on 13 species of migratory fish. The most significant feature of the results was the high content of histidine in these fish. The muscles of several species of fish contained appreciable amounts of anserine and carnosine. No balenine was detected in any of the species analyzed. These imidazole compounds, histidine, carnosine and anserine, accounted for over 50% of the total non-protein nitrogen.