Skeletal muscle protein is very important for protein and amino acid metabolism in the homeostasis of the whole body, because skeletal muscle accounts for the largest amount of tissue. Therefore, it is necessary to measure the rate of muscle protein synthesis and degradation. Urinary Nτ-methylhistidine (MeHis) is used as an index of myofibrillar protein degradation. It was demonstrated in this study using rats that 75% of MeHis in urine originated from skeletal muscle and that 25% originated from skin and intestine. Furthermore, it was suggested that there was a rapid turnover of myofibrils, because the specific radioactivity of MeHis in urine and muscle protein differed after administration of radioactive methionine. Several factors influencing muscle protein degradation were studied using MeHis release from perfused hindquarter muscles and isolated muscles. Insulin, known to be an anabolic hormone, it inhibited the degradation of muscle protein, particularly myofibrillar protein, in diabetic rats. Cysteine proteinases might be involved in muscle protein degradation, because leupeptin inhibited the release of MeHis and tyrosine from isolated muscle. Muscle protein degradation was also affected by the modification of muscle protein by active oxygen species or free radicals by feeding rats a vitamin E-deficient diet or iron overload. In these studies, a new method for determination of MeHis was developed, capable of measuring low concentrations of MeHis in plasma and medium. This method would allow acute changes in muscle protein degradation to be evaluated.

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It is well known that dietary xenobiotics and protein nutrition affect cholesterol and serum lipoprotein metabolism, although these precise mechanism has not been fully clarified. Treatment of rats with xenobiotics such as polychlorinated biphenyls (PCB) resulted in hyper-α-lipoproteinemia, characterized by an increase of apolipoprotein A-I (apo A-I) and replacement of apo E by apo A-I. Dietary PCB increased the hepatic levels of mRNA for apo A-I and HMG-CoA reductase. In hepatocyte culture, a direct effect of PCB on hepatocytes was revealed. The dietary level of protein regulated the expression of the liver apo A-I gene transcriptionally in a liver-specific manner. Soy protein isolate (SPI) decreased the cholesterol level of very-low-density lipoproteins and of high-density lipoproteins in comparison with casein. SPI lowered the level of apo E-rich lipoproteins, and then decreased that of apo A-I-rich lipoproteins. The hepatic apo A-I mRNA level was decreased by SPI, and elevated by addition of methionine. These results demonstrate that dietary xenobiotics and protein are regulators of apo A-I gene expression and the serum level of high-density lipoproteins.

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We investigated factors which influence the plasma levels of major carotenoids in 76 healthy persons (54 males and 22 females), and also examined the correlation between plasma carotenoid levels and smoking or drinking habits. Significant sex differences were shown in plasma levels of xanthophylls, α-carotene and retinol. The correlation between the plasma level of carotenoids having provitamin A activity and the plasma level of retinol was strongly negative. All plasma carotenoid levels and the plasma α-tocopherol level showed a slightly positive correlation. On the other hand, plasma levels of triglyceride, total-, LDL- and HDL-cholesterol showed a weak correlation with plasma carotenoid levels. Smoking had a tendency to reduce the plasma levels of carotenoids, whereas drinking did not.

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The ihhibitory effect of phytic acid (inositol hexakisphosphate: IP₆) on mineral availability is widely known. However, the effects of inositol phosphates (IP_n), which are intermediate products of phytate hydrolysis, are not clear. We have prepared IPn by enzymatic dephosphorylation of sodium phytate, and effects of inositol tetrakisphosphate (IP₄), inositol trisphosphate (IP₃) and inositol bisphophate (IP₂) on Ca, Mg and Zn availability were investigated as compared with an inorganic phosphorus compound (Na₂HPO₄) and IP₆ in growing rats for 4 weeks. Phosphorus from IP_2-4 was available as well as Na₂HPO₄ and their apparent absorptions of P were higher than that of IP₆. There was no difference in Ca absorption and retention among the experimental diets. Compared with IP₆, increased Mg and Zn absorption from diet containing IPn with fewer phosphorus groups was observed, and Mg retention with the IP₂ diet was even higher than with the Na₂HPO₄-containing diet. Our data suggest that inositol phosphates are a good dietary phosphorus source, and that inositol bisphosphate may have a significant effect on Mg and Zn availability.

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The addition of retinoic acid (RA, 2×10^-6M) to physiological saline solution markedly increased the activity of Ca²⁺ -dependent tissue transgiutaminase (TGase) (ca. 3.1-fold), which stabilizes newly formed protein assemblies at the synapse, in isolated rat superior cervical sympathetic ganglia, which are rich in synapses, fallowing in vitro aerobic incubation for 3h at 37°C. The RA-induced enhancement of ganglionic TGase activity was completely eliminated in the presence of either actinomycin D (1.0μg/ml), a depressor of transcriptional activity, or cycloheximide (10μg/ml), a potent inhibitor of protein synthesis. Kinetic studies showed that the stimulation of ganglionic TGase activity evoked by RA addition was associated with only an increase in the V_max value. Thus, the enzyme protein of TGase might be synthesized de novo in the ganglia in response to RA. These findings imply that RA also participates in phenomena involving synaptic activity such as memory.

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A study was undertaken to elucidate a useful method for extraction of edible proteins from green grasses. The materials for protein extraction were prepared from fresh grasses by treatment with cold acetone. The extractability of true proteins from each material was in the range 78.5-96.5% using hot 20% formic acid solution. However, true proteins were partly hydrolyzed by this treatment, and hence the practical yields of extracted true proteins were as follows: spinach 71%, bracken 72%, Equisetum arvense L. 71%, Leucaena glauca Benth 75%, Japanese cedar 73%. The extractabilities of true proteins from bracken and L. glauca Benth with this extractant were much higher than those with 5% organic acid solution, autoclaving at 120°C for 34 min or with several surface active agents.

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A study was undertaken to elucidate the extractabilities of true proteins from grasses using new protein extractants, i. e., 0.05 or 0.1N NaOH solution containing 80%-, 60%-, 40%-, 20%- and 0% acetone. The materials for extraction of true proteins were prepared from fresh grasses by treatment with cold acetone. The highest extractability of true proteins for each material was obtained by successive treatment with the above protein extractants. The values obtained were: spinach 84%, white clover 87%, Japanese radish leaf 91%, water hyacinth 96%, bracken 59%. True proteins of spinach and Japanese radish leaf were partly hydrolyzed by these treatments, and hence their practical yields were 69% and 65%, respectively.

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Euglena hydrolysate prepared from deffatted Euglena dry cells (Euglena glacilis Z) by treatment with pepsin was tested for inhibitory activity against angiotensin I converting enzyme (ACE) in serum and vascular tissues and for hypotensive effects in stroke-prone spontaneously hypertensive rats (SHRSP). The effect of captopril, an ACE inhibitor, was also studied in comparison. When Euglena hydrolysate was fractionated by gel filtration on Sephadex G-25 Fine, inhibitory activity was found in many Fractions, but Fraction D (molecular weight of the principle being approximately 2, 000) showed the strongest activity. The IC50 value of Fraction D to ACE (25mU/ml) from rabbit lung was 12μg protein/ml. The inhibitory activity of Fraction D was retained even after in vitro digestion by trypsin and chymotrypsin. When Fraction D wasorally administered to SHR and SHRSP for 8 days at a dose of 8mg protein/rat/day, pressure fell by about 30 and 20mmHg, respectively, from the original level. The serum ACE activity of SHRSP pon administration of Fraction D showed no difference from that of controls given 0.9% saline. In the SHRSP given captopril, the serum ACE activity was enhanced. The thoracic aorta ACE activity was lowered to a greater degree (p<0.05) in the Fraction D group and captopril group than in the control group. In the mesenteric artery, the ACE activity of Fraction D group was somewhat lower than that in the control group. The ACE activities of the thoracic aorta and mesenteric artery in the captopril group were significantly lower (p<0.05) than those in the controls. In perfused mesenteric artery isolated from SHRSP, Fraction D (500μg protein/ml) inhibited the contraction caused by angiotensin I (1μg/ml), as did captopril. These results suggest that the hypotensive effect of Fraction D in SHRSP is due to its inhibitive action on vascular tissue ACE activity.

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