Intracellular Distribution of Carnosine and Anserine in Skeletal Muscle.

The experiments of Bach and Langley (1) with frog muscle suspensions indicated that the carnosine of this tissue was freely diffusible upon dialysis of homogenates. On the other hand, Reddy and Hegsted (2) observed that the “debris” of rat skeletal muscle homogenates contained 43% of the total carnosine. This debris, representing material sedimented at 650 x g, still retained half of its initial carnosine content after extraction for 7 days in 50% glycerol at -10”. Mitochondria were found to contain over 7% of the total muscle carnosine, and this dipeptide was not removed by suspension of the granules in isotonic sucrose. Reddy and Hegsted concluded that bound carnosine was present within the muscle cell, although it was not clear whether the peptide was attached to myofibrils or whether the microsomes retained any of the carnosine. No results were reported for anserine, the more abundant of the two muscle dipeptides. Inasmuch as a selective binding of carnosine to subcellular components of muscle might offer a clue to the physiological role of this enigmatic peptide, it seemed desirable to further study the intracellular distribution of carnosine, and of anserine as well, in skeletal muscle tissue. We have not been able to confirm the conclusions of Reddy and Hegsted that relatively large concentrations of carnosine are associated with subcellular fractions of rat gastrocnemius muscle. However, by employing more sensitive isotopic labeling methods, it has been possible to demonstrate the retention of very small quantities of carnosine and anserine in certain cellular components of chick pectoral muscle. This tissue was chosen because of its unusually high dipeptide content (3). In addition to normal birds, experiments were performed with genetically dyst,rophic chicks.