Studies on protein turnover in chicken breast muscle

The aim of the project was to investigate the turnover of proteins in growing fowls; to thi^end, the fate of leucine in muscle was studied. Following the injection of Cor N-labelled leucine into growing broiler chickens, the specific content of this aminoacid was measured in plasma, total muscle protein, sarcoplasmic proteins and myofibrillar proteins, and in the separated enzymes aldolase, creatine phosphokinase, phosphoglycerate mutase and lactate dehydrogenase. The excretion of ^ N, derived from leucine, was also measured. For these measurements, the two forms of labelled leucine were injected together into 18 birds, and assays performed on muscle samples taken after killing the birds at six different time intervals, the longest being 72 hours after injection. Separation methods were developed that would yield the abovementioned enzymes in sufficient quantity for stable isotope analysis, and in a high degree of purity. A median purity ranging from 90% (for creatine ^hosphokinase) to 99% (for aldolase) was achieved. The specific activity of C, or atom percent excess of N, were calculated for each fraction, over the experimental period. Plots of labelling versus time were of an individual shape" for each protein or protein fraction. The results obtained indicate that established techniques of pulse-labelling may seriously underestimate the rate of protein synthesis. The physiological significance of these results is discussed.