1. Protein synthesis in liver and jejunal mucosa was measured in 19-d-old germ-free (GF) and conventional (CV) chicks fed on a semi-purified casein–gelatin (SCG) diet using a massive-dose single injection of [U-14C]phenylalanine. The effect of subsequent feeding for 9 d either a nitrogen-free (NF) diet or an NF diet supplemented with L-methionine (5 g/kg) and L-arginine hydrochloride (2 g/kg) (MA diet) was investigated in both types of chick.
2. In the liver, apart from the amount of DNA, the values for wet weight, protein, RNA, fractional synthesis rate (FSR) and the amount of protein synthesized were reduced after feeding the NF diet and, to a lesser extent, the MA diet. Except that the total amount of liver DNA was higher in the CV chicks than in their GF counterparts (P < 0·01), no environmental effect was significant. When expressed on a unit body-weight basis, liver weight, protein, RNA and DNA were significantly higher in the CV than in the GF chicks.
3. In the jejunal mucosa, the values for wet weight, protein and RNA tended to be reduced after the NF treatment but increased after the MA treatment. Mucosal DNA and the amount of protein synthesized (μg/mm per d) were significantly reduced after the NF diet but were less affected after the MA diet. Mucosal protein FSR and the amount of protein synthesized per mg RNA were significantly reduced after both dietary treatments. No difference was found among dietary treatments in the amount of protein synthesized per mg DNA in jejunal mucosa. Mucosal DNA was significantly higher in the CV chicks and the reverse was true for mucosal protein: DNA.
4. It was suggested that the increased protein synthesis in jejunal mucosa and possibly in liver on supplementation of an NF diet with methionine and arginine would partly, ifnot completely, account for the N-sparing effect of these amino acids.
5. Although the protein: DNA value was smaller in CV chicks, the FSR and the amount ofprotein synthesized tended to be higher than in their GF counterparts irrespective of nutritional status. This might imply that protein degradation rate is greater in the CV state.