Protein turnover of breast muscle in germ-free and conventional chicks

Abstract

1. The effect of the gut microflora on protein turnover in pectoral muscle (M. pectoralis profundus) was studied by means of dietary infusion of ~-[UJ~C]phenylalanine and of massive dose injection of ~-[4-~H]phenylalanine in chicks fed on a semi-purified casein-gelatin (SCG) diet until 19 d of age, and in those subsequently given either a nitrogen-free (NF) diet or N F supplemented with methionine and arginine (MA) for a further 9 d.2. Time-course changes in radioactivity released in expired carbon dioxide during the 8 h infusion period showed that isotopic equilibrium was reached in 4 h with the SCG diet and in 5 h with the MA diet. However, with the protein-deprived chicks given the N F diet, isotopic equilibrium was not achieved since radioactivity in CO, increased linearly throughout.3. On feeding the NF diet, fractional protein synthesis rate and the absolute amount of protein synthesized in chick breast muscle were reduced. These reductions were partially alleviated by supplementing the N F diet with methionine and arginine.4. The fractional degradation rate of breast muscle was increased in chicks given the NF diet, while the absolute amount of protein degraded was decreased. The addition of methionine and arginine counteracted these changes brought about by protein starvation.5. Generally speaking, the presence of the gut microflora had little, if any, effect on protein turnover rate in chick-breast muscle.

Changes in Breast Muscle Composition in the Young Chick

“…The RNA contents were similar to those obtained by Muramatsu et al (1985) and lower than those observed by Jones et al (1986a,b) at 2 and 3 wk of age. An inverse correlation was observed between the evolutions of breast muscle and body weights, and the evolution of RNA concentration values (r = -.93, P<.07; Tables 2 and 3).…”

“…and 4 wk of age and minimum values at 3 and 6 wk of age (P<05; Table 2). Values of RNA: DNA ratio described by Kang et al (1984Kang et al ( ,1985 and Muramatsu et al (1985) were similar to the ones obtained by the authors. Jones et al (1986a) reported a lower RNA:DNA ratio (5.4) at 2 wk of age.…”

“…Value of protein:DNA ratio described by Kang et al (1984) was smaller at 2 wk of age and larger at 5 wk of age than the ones obtained by the authors. Muramatsu et al (1985) and Jones et al (1986a,b) reported lower protein:DNA ratios at 2 wk of age.…”

“…These same authors (198S) have also studied the protein turnover and DNA and RNA levels in the breast and leg muscles of chicks from 1 to 8 wk of age. Muramatsu et al (1985) have observed the effect of gut microflora on protein turnover in breast muscle. Jones et al (1986a,b) have described variations in the muscle protein metabolism between broiler and layer chicks at 2 wk of age and between normal broiler and dwarf broiler chicks at 2 and 3 wk of age.…”

Responses to nutrients in farm animals: implications for production and quality

“…A positive effect of methionine supplementation on muscle growth has conversely been reported, since the addition of methionine to a methionine-deficient diet, otherwise balanced in terms of other amino acids, increases accretion and synthesis of protein in the gastrocnemius and pectoralis major muscles in chickens (Barnes et al, 1995). Methionine supplementation in a protein-free diet is also effective in increasing protein synthesis of whole-body protein, particularly muscle protein (Muramatsu et al, 1985 and. Webel and Baker (1999) found that cysteine supplementation elicits a response similar to or greater than methionine and suggested that the primary need is for cysteine, and not for methionine per se; like methionine, cysteine is an important constituent of feather and fur proteins.…”