The pyrimidine moiety of thiamin can be synthesized in bacteria from 5-aminoimidazole ribotide (AIR), an intermediate in purine biosynthesis. To transform the imidazole ring of AIR to the pyrimidine, the bond between C-4 and C-5 of the imidazole ring should be ruptured and a two-carbon unit should be inserted. We investigated a precursor of the two-carbon unit which should be inserted to form the pyrimidine. To examine the possibility of the twocarbon compound as a precursor which is formed from a three-carbon intermediate in the glycolytic pathway and its three-carbon derivative by decarboxylation in cells, we studied the incorporation of [2-14C]glycerol, [2-14C]pyruvate, [U-14C]alanine and [3-14C]serine into the pyrimidine by Escherichia coli. Glycerol, pyruvate and alanine were not incorporated into the pyrimidine. Radioactive carbon of [3-14C]serine was incorporated into C-2 of the pyrimidine via one-carbon units pool. Then, we investigated the possibility of a ribose moiety of AIR being a precursor of the two-carbon unit. As ribose has low permeability into E. coli cells, the ribose moiety of AIR was labeled with [14C]glucose which was added to the growth medium. The results show that two radioactive carbons of [U-14C]glucose were incorporated into the pyrimidine and radioactive carbon of [6-14C]glucose was incorporated into hydroxymethyl carbon attached to C-5 of the pyrimidine. The dilution rates of the specific radioactivity of the pyrimidine from [U-14C]glucose and [6-14C]glucose well coincide with those of the ribose moiety of the nucleotide (AMP). Radioactive carbon of [1-14C]glucose was not incorporated into the pyrimidine and nucleotide. It is concluded that the two-carbon fragment derived from C-4' and C-5' of the ribose moiety of AIR can be incorporated into the pyrimidine moiety of thiamin as the precursor of C-5 and hydroxymethyl carbon.
Diurnal changes in glycogen stores of adipose tissues and in vitro lipolytic activity of isolated epididymal fat cells, and their lipolytic responsiveness to epinephrine and theophylline were examined in rats adapted to a 2-h daily meal feeding (20.00-22.00 h; darkness between 20.00-08.00 h) for 3 weeks and in control rats fed ad libitum. The fat cells from both groups of animals showed the peak of lipolytic activity at the mid-dark period (03.00 h), but the peak values and the average values at 6 or 7 time points examined within the 24-h feeding cycle were significantly higher (p<0.025) in meal-fed rats. Basal, epinephrine-stimulated, and epinephrine-induced lipolysis of fat cells from control rats showed diurnal changes, and the rhythms and their amplitude were affected by meal feeding. Changes in lipolytic activity of fat cells did not seem to relate directly to those of glycogen stores in adipose tissue. The over-all 24-h means of lipolytic activity of fat cells were significantly increased (p<0.001) with meal feeding. Mean cell size of epididymal fat pads was significantly smaller (p<0.001) in meal-fed rats, but lipolytic responsiveness to the graded concentrations of epinephrine and theophylline in the incubation medium was significantly greater (p<0.001) in meal-fed rats than in rats fed ad libitum. Thus, these findings suggest that lipolytic activity of the CAMP-hormone sensitive lipase system in fat cells might be increased with meal feeding, in rats. Furthermore, the present results may give a new idea to consider the discrepancy that many workers have not been able to observe the increase in body fat deposition with meal feeding, which has been frequently reported to enhance lipogenesis in rats.
This study was undertaken to investigate the changes incarnitine metabolism in rats and mice injected with T4 for 3 days and 10 days, respectively, and in rats fed a T3 and T4-supplemented diet for 6 weeks. Thyroid hormone administration brought about a significant in crease in urinary excretion of total carnitine. In T3 +T4-treated ratsurinary esterified-carnitine to free-carnitine ratio increased significantly inthe later phase of administration. Carnitine pool size in the body was sig nificantly decreased in both T4-injected mice and T3 +T4-fed rats. In thelatter animals, this decrease was due to the reduced carnitine contents inorgans other than the liver, especially in skeletal muscle. The amount ofcarnitine synthesized by control and T3 + T4-treated rats was calculatedfrom the data on carnitine intake, urinary carnitine excretion and carni tine pool size in the body over the 6-week period. Values obtained were 66.2±3.2 (mean±SEM) μmol/rat and 28.5±4.9 μmol/rat, respectively, and the difference was significant (p<0.05). These results indicate thatcarnitine synthesis is depressed by thyroid hormone, however, some pos sibilities that thyroid hormone may increase carnitine synthesis were alsodiscussed.
The effect of protein-energy malnutrition on Biliary immunoglobulins was investigated in rats fed isocaloric diets containing 0.5%, 5%, and 18% casein, respectively. Growth was severely retarded in rats fed 0.5% casein diet and moderately in rats fed 5% casein diet, and these groups had decreases in serum albumin and total protein levels. Since the energy intake was low in rats fed protein-insufficient diets, the nutritional status was defined not as protein malnutrition but protein-energy malnutrition. Depression of systemic immune functions in protein-energy malnourished rats were demonstrated by serum IgG and IgA levels, and antibody responses to dinitrophenylated bovine gamma globulin, a T-cell dependent antigen. The depressed systemic immune functions observed in those rats were suggested to be caused by thymic atrophy. IgA levels in bile were much higher in all groups than IgG levels. IgG levels decreased in rats fed 0.5% casein diet but not in rats fed 5% casein diet, while IgA levels decreased in rats fed 5% and 0.5% casein diet relating to casein levels. The ratios of IgA to IgG in bile also decreased in rats fed protein-insufficient diets. By sucrose density gradient centrifugation secretory IgA levels in bile were shown to decrease in rats fed 0.5% casein diet, suggesting that the secretion of IgA by hepatic parenchymal cells is depressed in the protein-energy malnourished rats.
Effect of partial hydrolyzate of casein and soybean protein on serum lipoproteins and fecal neutral steroids in cholesterol-fed rats was studied. In rats fed partial hydrolyzate of casein, the levels of plasma and liver cholesterol, liver triglyceride and the ratio of serum β/α lipoprotein had a tendency to decrease compared with those in rats fed intact protein. On the other hand, no difference was observed between soybean protein and partial hydrolyzate of soybean protein diet groups. The excretion of neutral steroids to feces and the amount of fecal coprostanol were increased in rats fed soybean protein and partial hydrolyzate of soybean protein.
The effect of soybean protein on coprostanol production and cholesterol metabolism was studied in cholesterol-fed rats. Plasma cholesterol was decreased in the soybean protein diet group compared to the casein diet group. Although coprostanol was produced more in rats fed soybean protein than in those fed casein, no difference was observed in the levels of total neutral steroids at any part of the intestine. The activity of microbial conversion from cholesterol to coprostanol was evidently high in rats fed soybean protein. The total amount of neutral steroids excreted in feces had a tendency to increase. These data seem to indicate that the increase of the unabsorbed soybean protein causes the increase of intestinal coprostanol production.
Obligatory urinary and fecal N losses in young Japanese women were evaluated and the effect of energy intake on the utilization of rice and egg mixed protein was investigated in subjects receiving a low protein diet. Seven female students were given a protein-free diet for ten days. Feces and 24-h urine samples were collected throughout the period and their nitrogen contents were analyzed. Basal metabolism was measured and the lean body mass was calculated from urinary creatinine excretion by the equation of Forbes. The mean weight loss of the 7 subjects during the ten days was 1.5 kg, the mean obligatory urinary N loss was 32.3±5.9mg/kg body weight, 1.67±0.45 mg/kcal basal metabolism, or 1.68±0.32g/g creatinine, and the mean obligatory fecal N loss was 10.1±2.0mg/kg body weight, or 0.51±0.08 mg/kcal basal metabolism. In a second experiment, 17 female subjects were divided into three groups with an energy intake of about 35, 42, 46kcal/kg BW, respectively. During the 7-day experimental period, they were given a low protein diet containing 250g of rice and 125g of whole egg. The nitrogen contents of the 24-h urine samples and feces collected were analyzed and the nitrogen balance was calculated as the difference between N intake and urinary and fecal N excretion. Subjects with an energy intake of 35 kcal/kg BW had a negative N balance, while subjects with an intake of 46 kcal/kg BW achieved an apparent positive N balance. The NPU values of rice and egg mixed protein with energy intake of 35, 42, 46 kcal/kg BW were calculated from the N balance data and the values for obligatory urinary and fecal N losses in the first experiment as 25, 37 and 54, respectively.
The present studies were conducted to characterize the relevance of a microsomal mixed function oxidase system to the polychlorinated biphenyls (PCB)-induced vitamin A reduction and endogenous lipid peroxide formation in the liver of rats. And also, this study dealt with an influence of scavengers on the hepatic lipid peroxide formation stimulated by PCB. Rats were given a 0.01% PCB diet supplemented with adequate nutrients, for 14 days. In an experiment, secobarbital was injected subcutaneously for the degradation of hepatic microsomal cytochrome P-450 heme. A marked liver enlargement and a significant increase of total liver lipid content were observed in the PCB group. The secobarbital enhanced the PCB-induced liver enlargement but no effect of secobarbital on the lipid content was recognized. PCB significantly induced hepatic microsomal cytochrome P-450, but not both cytochrome b5 and NADPH-cytochrome c reductase. The secobarbital suppressed the induction of cytochrome P-450 caused by PCB to approximately one-half. The hepatic vitamin A content significantly decreased on PCB administration and the secobarbital slightly enhanced the PCB-induced vitamin A reduction. However, the vitamin A content in the secobarbital-injected control group decreased to nearly the same levels as in the PCB groups. Therefore, it was presumed that the hepatic microsomal mixed function oxidase system, especially the cytochrome P-450, was possibly not directly involved in the PCB-induced hepatic vitamin A reduction or that a metabolic system related to mixed function oxidase system was involved in the reduction. On the other hand, the hepatic lipid peroxide content tended to increase on PCB administration though no significant difference was recognized. In contrast, the hepatic lipid peroxide content significantly increased in the secobarbital-injected PCB group as compared with the secobarbital-injected control group. However, there was no difference in the lipid peroxide contents between the control groups with and without the injection of secobarbital, and also between the PCB groups. The hepatic vitamin E contents lowered in the secobarbitalinjected groups but no effect was observed on PCB administration. The glutathione peroxidase activity decreased significantly on PCB administration and the secobarbital further decreased the activity. Therefore, it was suggested that the significant increase and tendency of increase in hepatic lipid peroxide contents in the PCB groups with and without injection of secobarbital were ascribed to an insufficiency of lipid peroxide scavengers in the liver. And also, it was supposed that the degradation of hepatic microsomal cytochrome P-450 heme caused by secobarbital was not responsible for the hepatic lipid peroxide formation on PCB administration, indicating that the cytochrome P-450 was possibly not directly involved in the PCB-induced hepatic lipid peroxidation.
The mode of DNA-breaking actions of ascorbic acid (AsA) and triose reductone (TR) in the presence of Cu2+ was studied by use of 0.8% agarose slab gel electrophoretic analysis. The DNA-breaking actions of the mixture of AsA or TR and Cue + were inhibited by N2 gas, hydroxyl radical scavengers and catalase, indicating that the oxidation of AsA or TR by Cu2+ and the hydrogen peroxide and hydroxyl radicals resulting from the oxidation are essential for the fragmentation of DNA by the mixture of AsA or TR and Cu2+. However, the DNA-breaking activity of these reductones varied with pH, while their oxidation rates were proportional to the increase in pH. The marked fragmentation of DNA occurred at pH 4, 7 or 8. The breakages of DNA by AsA or TR in the presence of Cu2+ were concluded not to be associated with the oxidation rates of reductones.
The role of Cu2+ on the DNA-breaking action of ascorbic acid (AsA) and triose reductone (TR) was studied with an agarose slab gel electrophoretic analysis. AsA and TR decomposed calf thymus DNA which had been pretreated with Cu2+, and their decomposing activity was proportional to the concentration of Cu2+ bound to the DNA. The DNA-Cu2+ complex had the ability to oxidize reductones. AsA and TR also decomposed the pretreated DNA with Cu2+ more markedly than that pretreated with Cu2+ and successively with EDTA. The DNA-breaking activity of AsA and TR showed no Cu2+-concentration dependency. The maximal fragmentation of DNA occurred at the concentration ratio of DNA and Cu2+ of 4: 1. Excess concentration of Cu2+ decreased the activity of reductones. The present results indicate that the binding of Cu2+ to DNA molecules is also essential for the DNA-breaking action of AsA and TR in the presence of Cu2+ and that Cu2+ bound to DNA molecules has more effective promoting activity than free Cu2+
Three diets based on rice-dehulled mungbean, rice-minced meat and rice-mungbean with hull were tested with infants 11 to 20 months of age using a short term nitrogen balance technique. The results indicate that with isocaloric and isonitrogenous intake, all the subjects given either of the three diets were in positive nitrogen balance. The protein quality, in terms of nitrogen absorption and true digestibility, of rice-meat diet was superior to that of rice-bean diets. Among the rice-bean diets, it was noted that rice-mungbean with hull had a lower digestibility as compared to rice-dehulled mungbean diet. The poor digestibility of ricemungbean with hull diet is the first limiting factor in its utilization by infants. Dehulling of mungbean before cooking is recommended for preparing weaning food for infant feeding.