Comparison of human myofibrillar protein catabolic rate derived from 3-methylhistidine excretion with synthetic rate from muscle biopsies during L-[alpha-15N]lysine infusion.
1. Urine was collected in five healthy men over 10--14 days, with fasting blood samples on days 1, 5 and 10, whilst they consumed a standard creatine-free diet, which was quantitatively related to their body surface area. 2. The urinary excretion of 3-methylhistidine fell to a plateau by day 5 in all subjects. Myofibrillar protein catabolic rate calculated from the mean value of 3-methylhistidine excretion from day 5 to day 10 averaged 1.21 g day-1 kg-1 body weight. The average turnover of muscle myofibrillar protein was calculated to be 2.16%/day. 3. From a previous study using continuous intravenous infusion of L-[alpha-15N]lysine with serial muscle biopsies on the same subjects, the mean myofibrillar protein synthetic rate was calculated to be 0.82 g day-1 kg-1 body weight, and the mean turnover rate was 1.47%/day of total muscle myofibrillar protein. 4. The estimations of myofibrillar protein turnover rate derived from the two methods are compared and the differences discussed.
D000328:Adult; D003404:Creatinine / Q000652:urine; D006639:Histidine / Q000031:analogs & derivatives*; D006801:Humans; D008239:Lysine / Q000378:metabolism; D008297:Male; D008762:Methylhistidines / Q000652:urine*; D008875:Middle Aged; D009124:Muscle Proteins / Q000096:biosynthesis / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism*; D013997:Time Factors
D008762:Methylhistidines; D009124:Muscle Proteins; D006639:Histidine; D003404:Creatinine; D008239:Lysine