1. Critical studies on the distribution of NT-methylhistidine (3-methylhistidine; Me-His) among organs and tissues in adult rats are reported. Adult rats contained 46.5 ± 3.6 mg Me-His/kg body-weight. Almost 90% of the Me-His in the body was recovered from skeletal muscle. These results support the hypothesis that fractional catabolic rates of myosin and actin in skeletal muscle can be estimated by measuring urinary excretion of Me-His.2. Dietary protein level did not affect the total amount of Me-His in the body. However, urinary excretion of Me-His increased as dietary protein intake was increased.3. From these results it was concluded that fractional catabolic rates of myosin and actin increase as dietary protein intake increases.

I . Distribution of N'-methylhistidine (3-methylhistidine; Me-His) among organs and tissues in cattle was determined. From the amount of Me-His in skeletal muscle protein and daily urinary output of Me-His, fractional catabolic and synthetic rates of myofibrillar proteins of skeletal muscle during growth were calculated.2. More than 93.4% of the total Me-His (35.6 mg/kg body-weight) in the analysed cattle tissues occurred in skeletal muscle protein. The amount of Me-His in tissues other than skeletal muscle was relatively small. Daily urinary excretion of Me-His in the cattle which were fed on hay and concentrate was 135 mg at a growing stage of 217 kg body-weight and 145 mg at a stage of 312 kg. The Me-His content of foodstuffs was also carefully checked in the present investigation. Assuming that absorbed dietary Me-His is quantitatively excreted in the urine without delay, the contribution of Me-His in foodstuffs was calculated to be approximately 30 % of the urinary Me-His. Rumen protozoa and bacteria contained little Me-His.3. From these results, fractional catabolic and synthetic rates of myofibrillar proteins of the cattle at a growing stage of 217 kg body-weight were calculated to be 1.22 %/d (half-life 56 d) and 2.73 %/d, while these rates at a stage of 312 kg body-weight were 1.02 %/d (half-life 67 d) and 1.51 %/d respectively. These values were calculated on the same assumptions as those for the rat (Young er Funabiki et al. 1976).Of the Me-His present in foodstuffs 94 yo was tentatively assumed to be excreted into urine.Estimation of synthetic and catabolic rates of skeletal muscle proteins of domestic animals is very important for studying whole-body protein metabolism.Perry (1974) estimated synthetic and catabolic rates of muscle proteins of piglet. Buttery et al. (1975) showed that the fractional turnover rate of muscle protein in sheep is 1.7%/d (half-life 40.7 d). However, there have been no reports of studies of the turnover rates of myofibrillar proteins of skeletal muscle in cattle.The turnover rate of myofibrillar proteins is often calculated from urinary excretion of N7-methylhistidine (3-methylhistidine; Me-His) in the instance of small animals, as well as man (Young et al. 1972;Long et al. 1975;Haverberg, Deckelbaum et al. 1975;Funabiki et al. 1976;Nishizawa et al. 1977; Nishizawa, Shimbo et al.

1. Fractional flux rates of N%nethylhistidine (3-methylhistidine; Me-His) of skin and gastrointestine were measured by administering [methyl,H]methionine to rats.2. The results showed that the contribution of these tissues to urinary excretion of Me-His was at least 16.6 %. This means that when fractional catabolic rates of myosin and actin were estimated from urinary excretion of Me-His, the part of Me-His derived from skin and gastrointestine should not be neglected.The method to measure the fractional catabolic rate of myosin and actin in skeletal muscle by urinary excretion of NT-methylhistidine (3-methylhistidine; Me-His) has been shown to be valid by several investigators ( . If the flux rates of Me-His in these tissues are greater than that in skeletal muscle, we have to take into account the amount of urinary Me-His released by these two tissues. The present work was undertaken to determine the fractional flux rates of Me-His in skin, gastrointestine and skeletal muscle by administering [methyl-SH]methionine to rats. Results showed the significant contribution of skin and gastrointestine to the excretion of Me-His into the urine. M E T H O D SSixteen Wistar male rats weighing 197-260 g were individually housed in stainless-steel cages in an air-conditioned room maintained at 22+ I". They were given a diet with 200 g casein, 50 g soya-bean oil, 40 g salt mixture, 8.5 g vitamin mixture, 1.5 g choline chloride and 700 g maize starch/kg. The salt and vitamin mixtures were prepared according to Harper (1959). Food intake was restricted to 12 g/d per rat as in a previous paper (Nishizawa et al. 1977). After 7 d the animals were administered intraperitoneally 26 pCi ~-[methyl-~H]methionine (specific radioactivity 200 mCi, New England Nuclear, Boston) per kg body-weight. This radioactive amino acid was dissolved in saline (9 g NaCI/l). On the first, third, seventh, fourteenth and twenty-first days after the administration of the radioactive methionine, the animals were lightly anaesthetized with diethyl ether and killed by exsanguination. The hind limb muscles and gastrointestinal tract were removed https://www.cambridge.org/core/terms. https://doi

Proso millet (Panicum miliaceum) is a more minor crop than foxtail, finger and pearl millets, but it is grown for humanconsumptionin someAsian and African countries. Recently, we have reported that the nutritional quality of proso millet protein is poor but the quality can be greatly improved by supplementing with lysine and threonine.M any studies have shown that vegetable proteins, es

No abstract