The growth rates of young chicks were varied from 0 to 10% per day by manipulation of the adequacy of the amino acid and energy supply. The rates of protein synthesis in the white breast (pectoralis thoracica) muscle and the dark leg (gastrocnemius and peronaeus longus) muscles were estimated by feeding l-[U-(14)C]tyrosine in amino acid/agar-gel diets (;dietary infusion'). This treatment rapidly and consistently produced an isotopic equilibrium in the expired CO(2) and in the free tyrosine of plasma and the muscles. Wholebody protein synthesis in 2-week-old chicks was estimated from the tyrosine flux and was 6.4g/day per 100g body wt. In 1-week-old chicks the rate of protein synthesis was more rapid in the breast muscles than in the leg muscles, but decreased until the rates were similar in 2-week-old birds. Synthesis was also more rapid in fast-growing Rock Cornish broilers than in medium-slow-growing New HampshirexSingle Comb White Leghorn chicks. No or barely significant decrease in the high rates of protein synthesis, in the protein/RNA ratio and in the activity of RNA for protein synthesis occurred in non- or slow-growing chicks fed on diets deficient in lysine, total nitrogen or energy. Thus the machinery of protein synthesis in the young chick seems to be relatively insensitive to dietary manipulation. In the leg muscles, there was a small but significant correlation between the fractional rate of growth and protein synthesis. A decrease in the fractional rate of degradation, however, appeared to account for much of the accumulation of muscle protein in rapidly growing birds. In addition, the rapid accumulation of breast-muscle protein in rapidly growing chicks appeared to be achieved almost entirely by a marked decrease in the fractional rate of degradation.

The concept of a labile protein reserve is based on the relatively slow establishment of a new equilibrium in the rate of nitrogen excretion after an abrupt change in dietary supply. The evidence reviewed shows that a majority of this nitrogen is derived from or deposited in skeletal muscle proteins. The rates of synthesis and degradation of total body protein are rapid in large animals (man and swine) and are correlated with heat production. The rate of protein synthesis in skeletal muscle greatly exceeds the rate of growth and is sensitive to nutritional status. The rate exceeds the rate of degradation in response to the ingestion of an adequate diet so that tissue proteins are accumulated, but it decreases below the rate of degradation under conditions of deprivation. In this latter state, proteins of skeletal muscle supply amino acids for energy or for the synthesis of other more essential proteins, e.g., milk proteins during lactation. Thus, we conclude that the labile protein reserve is a product of the normal, dynamic metabolism of protein.

The curve for decay of 14C in rat liver protein labelled by injection of NaH14CO3 was analysed to obtain the average turnover rate of mixed liver protein. Three different methods of analysis were used. (1) Unlike decay curves from homogeneous proteins, the curve did not fit a single exponential, but a good fit was obtained with three exponentials. By assuming that the mixture contained three major components with different turnover rates, the calculated value for the average turnover rate (k) was close to 40% per day. (2) k was also calculated from the area under the decay curve, a method which makes no assumptions about the number of proteins in the mixture. This method also gave a value close to 40% per day. (3) It was shown empirically, both by simulation of decay of label in model mixtures of protein and with the decay curve measured in vivo, that k can be calculated from the time taken for the specific radioactivity to fall to 10% of its maximum value. This is an advantage, since the other two methods require the decay curve to be measured over a much longer period of time.

Rates of synthesis and breakdown of body protein and oxidation of leucine were measured in six obese subjects by constant intravenous infusion of (1 14C)leucine for 24-hr periods. During the night, when no food was given, the rate of whole body protein synthesis was 67% of the rate observed furing the day, when food was given hourly. By contrast the rate of body protein breakdown remained constant over the full 24 hr. This resulted in the immediate deposition of about 30% of the protein intake during the day, whereas the remaining 70% was immediately oxidized. At night the rate of protein oxidation fell to only 38% of its daytime value. The rate of oxygen consumption also decreased at this time so that the contributon of protein oxidation to total energy expenditure fell from 27% during the day to 13% at night. These changes reflect the normal, discontinuous pattern of food intake and the need during feeding to store protein in tissues for use in subsequent periods of fasting.

Relative to rats fed a 15% protein-diet, 300-g rats fed a 5% protein-diet for 5 weeks consumed 19% more food but gained only 28% as much weight, showed twice the thermic response when fed, had twice as much subscapular brown adipose tissue with almost twice the specific GDP-binding activity. There was no difference between these groups in skeletal growth nor, unexpectedly, in the proportion of carcass fat.

Growth and protein turnover were examined in the breast (pectoralis thoracica) and the leg (gastrocnemius-peroneus) muscles of broiler chicks at 1, 2, 4, and 6 weeks posthatching. The fractional rate of protein synthesis (ks) was measured by an isotope emulsion method. The fractional degradation rate (kd) was calculated from the difference in ks and fractional deposition rate (kg), which was estimated from regression equations of muscle size and protein content on body weights. The growth rate (%/day) of skeletal muscle exceeded that of the whole body. Muscle growth involved an increase in the total deoxyribonucleic acid (DNA) and the DNA-unit size and a subsequent decrease in the concentrations of nucleic acids without alteration in the ribonucleic acid (RNA):DNA ratio and RNA and DNA activity. The ks in breast muscle protein fell markedly from 48 to 16%/day between 1 and 6 weeks posthatching, whereas in leg muscle, ks underwent a more gradual decrease; from 36 to 17%/day during the same period. These changes resulted mainly from the reduction of DNA and RNA concentrations with age. The kd decreased only slightly between 1 and 2 weeks in the both muscle groups. The kg also showed a developmental fall from 33 to 4%/day and from 21 to 4%/day in the breast and leg muscles, respectively, during the 5-week period.(ABSTRACT TRUNCATED AT 250 WORDS)

BIOCHEMISTRY: SWICK AND WOOD PROC. N. A. S. sumption that the structure of prodigiosin is correctly represented in Figure 1. Furthermore, inspection of the prodigiosin molecule suggests that at least the methoxyl-bearing ring may be derived directly from hydroxy-proline.Summary.-Glycine-2-C 4 was incorporated into prodigiosin, the red pigment of Serratia marcescens, in confirmation of the results of Hubbard and Rimington. 5-Aminolevulinic acid-5-C'4 was, however, not incorporated showing that the 3 pyrrole rings of prodigiosin must be derived from a precursor other than porphobilinogen, the pyrrolic precursor of porphyrins. Experiments with L-proline-C'4 indicated that proline or a closely related metabolic derivative is a precursor of prodigiosin.The evidence that propionibacteria form propionate by the direct decarboxylation of succinyl CoAl has been reviewed by Wood et al.2 It has generally been considered that carbohydrates, e.g., glucose, glycerol, etc. are catabolized to pyruvate which is then converted to oxalacetate by the fixation of carbon dioxide. Oxalacetate is reduced to succinate, which in turn is esterified with CoA and decarboxylated to propionyl CoA and CO2. Therefore the reduction of one mole of pyruvate to propionate would be expected to involve the fixation and release of one mole of CO2.

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