MUSCLE PROTEIN TURNOVER IN CHICKENS VARYING IN MUSCLE MASS AND GROWTH POTENTIAL (SYNTHESIS, DEGRADATION, METHYL-HISTIDINE)
Abstract
Experiment 1. Dietary infusion was used to estimate fractional protein synthesis rates (FSR) of muscle in broiler and layer chicks. Six 2-wk old birds of each strain were given a diet containing 2 Ci L-(U-('14))-tyrosine for 6 h. Birds were sacrificed and the pectoralis major (PM) and two combined leg muscles (LM) were analyzed. Fractional accretion rates (FAR) were determined from muscle protein accumulation data of subgroups of birds. Fractional degradation (FDR) was obtained by difference (FAR=FSR-FDR). Relationships between protein, RNA and DNA concentrations and FSR were studied. FSR in the PM of layers was similar to broilers and to PM to both strains. FDR was higher in layer than broiler muscles. RNA activity of layer PM was lower (P < .05) than the other muscles. DNA activity was lower (P < .05) in PM of both strains compared to LM. In conclusion differences in FAR between the two strains of birds were caused by higher FSR in the PM and lower FDR in broiler muscle. Experiment 2. FSR and FDR were estimated in dwarf and normal broiler chicks using methods described in experiment 1. Five two-wk old and five 3-wk old birds of each genotype were used. Two-wk old chicks, dwarf chicks and PM muscles had higher (P < .05) FSR than 3 wk-old chicks, normal chicks and LM respectively. Two-wk old chicks and dwarf chicks had higher FDR than 3-wk old chicks and normal chicks respectively. There was a decrease (P < .05) in RNA concentration and RNA activity from 2 to 3 wk. RNA concentration was higher (P < .05) in dwarf than normal birds and in the then LM. These results indicate that protein turnover in dwarf chickens was greater than in normal chickens and decreased with increasing age. Experiment 3. Three methyl-histidine (3 Me-His) concentration was determined in various tissues and organs, and the excreta of six 2-wk old broiler chicks. Three Me-His content was determined in tissues and organs by amino acid analysis. Excreta were collected for a 24 h period and 3 Me-His was quantitated to determine FDR of muscle. Muscle contained most of the 3 Me-His in the body. These results indicate that muscle is the major source of 3 Me-His in the body. FDR determined by 3 Me-His excretion was about one half that of the infusion method. The difference was attributed to slow turnover rate of actin.
Degree
Ph.D.
Subject Area
Livestock
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