Estimation of the fractional breakdown rates of myofibrillar proteins in chickens from quantitation of 3-methylhistidine excretion.
The objective of this study was to estimate the fractional breakdown rate (FBR) of muscle protein in the chicken from measurements of 3-methylhistidine (3-Mehis) excretion and the amount of 3-Mehis bound in the skeletal muscle pool. Excreta were collected for a 24-hr period from six 2-week-old broiler chicks that were fed a purified diet, and 3-Mehis was quantified. The concentration of 3-Mehis was determined in the dissected tissues of skeletal muscle, heart, gizzard, intestine, crop, stomach, brain, lung, kidney, liver, skin, feathers, and skeleton. Detectable amounts of 3-Mehis were not found within serum either before or after acid hydrolysis. Heart, gizzard, intestine, crop, and stomach contained considerable amounts of 3-Mehis, but because of their small contribution to body weight, they contributed only 11% of the total body 3-Mehis. Muscle contributed 84% of the 3-Mehis in the body. Muscle protein FBR determined from 3-Mehis excretion was 5.3%/day, about half that estimated using continuous infusion methods. The difference between the two quantification methods was attributed to the slow turnover rate of actin, which contains most of the 3-Mehis.
D000818:Animals; D002645:Chickens / Q000378:metabolism*; D005243:Feces / Q000032:analysis; D006639:Histidine / Q000031:analogs & derivatives*; D008297:Male; D008762:Methylhistidines / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism*; D014018:Tissue Distribution
D008762:Methylhistidines; D009124:Muscle Proteins; D006639:Histidine; C028118:3-methylhistidine