The effects of high dietary protein and nitrogen levels on the preformed methyl group requirement and methionine-induced growth depression in chicks

The chick's choline and methionine requirements are both increased by high dietary protein level. Studies were conducted to test the hypothesis that the chicks' need for preformed methyl groups is increased by high protein diets (not methionine or choline per se). Chicks fed 25% isolated soybean protein (ISP) diets responded to methionine supplementation (162 vs 110 g gained in 14 days) but not to choline (119 g vs. 110 g), while those fed 50% ISP responded to either methionine (174 g vs. 126 g) or choline (181 g vs. 126 g) supplementation. Further, neither cystine nor homocystine could replace methionine in improving the growth of chicks fed the high protein diet. In other experiments, L-methionine and betaine HCl were found to alleviate the growth depression caused by excessive levels of L-glutamic acid. Excessive levels of L-methionine had a protective effect against growth depression caused by L-glutamate and diammonium citrate, and conversely, supplementary L-serine and sodium formate were not protective against glutamic acid- or arginine-induced growth depression. The results are consistent with the hypothesis that the preformed methyl group requirement is increased by high levels of dietary protein and excessive nitrogen from a single amino acid.

Blood and tissue branched-chain amino and alpha-keto acid concentrations: effect of diet, starvation, and disease

Branched-chain alpha-keto and amino acid (BCKA, BCAA) concentrations were measured in blood, plasma, and tissues of rats fed low protein (8% casein) or high protein (60% casein) diets; and in rats fed a stock diet and subjected to 3 days of starvation of chemically-induced diabetes. Concentrations of these amino and ketoacids were also measured in blood from patients with maple syrup urine disease. Valine, isoleucine, and leucine concentrations in blood from rats fed the stock diet were 124 +/- 7, 58 +/- 4 and 99 +/- 5 microM, respectively. Blood BCAA concentrations of rats fed the high protein diet and diabetic rats were elevated 2- to 3-fold; small increases were observed in blood from starved rats. Changes in blood BCAA concentrations paralleled those in tissues, except in starved rats in which the skeletal muscle free BCAA pool increased proportionately more than the circulating pool. Mean blood BCKA concentrations of rats fed the stock diet were low--7.9 +/- 0.5, 7.1 +/- 0.4 and 12.4 +/- 0.7 microM for alpha-ketoisovaleric, alpha-keto-beta-methylvaleric, and alpha ketoisocaproic acids, respectively. All treatments resulted in increases in blood BCKA concentrations of from 1.4 to 2 fold. In liver and heart, concentrations of BCKA, except for that of alpha-ketoisocaproic acid were near the limits of detection (less than 1 nmole/g). There was significant accumulation of all three BCKA in skeletal muscle which was estimated to contain about 80% of the measured body free BCKA pool. Blood BCKA are well regulated. Only in patients with maple syrup urine disease are plasma concentrations of BCKA useful indicators of altered tissue BCAA metabolism. Skeletal muscle, where oxidation of the BCKA is limited by low BCKA dehydrogenase activity, would seem to be the major source of circulating BCKA.

Factors influencing the assessment of the availability of choline in feedstuffs

Experiments were conducted to test the hypothesis that chicks fed diets designed to be first-limiting in choline will also respond to supplements of sulfur-containing amino acids and that the growth response of chicks fed a choline-limiting diet to a supplement of a feedstuff cannot be accepted as a reliable measure of the choline content of the feedstuff. Chicks fed 25% isolated soybean protein (ISP) diets that were severely limiting in choline showed a growth response to supplements of either choline or methionine. A bioassay was used to determine the availability of choline in soybean meal (SBM). Results indicated that including 10% SBM in the 25% ISP diet (at the expense of corn starch) drastically altered the chicks' response to choline. When 100 ppm choline was added to the 10% SBM diet, growth responses, compared to the original standard curve, indicated recoveries of 400 and 352% in two experiments. Additional studies indicated that chicks fed the 25% ISP + 10% SBM-based diet responded not only to choline additions but also to methionine, cystine, sulfate, and betaine additions. Further, it was shown that chicks fed a practical-type corn-soy-grease-based diet respond equally as well to supplements of 1% concentrated Steffens Filtrate, .2% L-methionine, or 800 ppm choline. The validity of assays of choline availability based on the assumption that choline is the first-limiting nutrient is questioned.

Excretion of tryptophan-niacin metabolites by young men: effects of tryptophan, leucine, and vitamin B6 intakes

Three human metabolic studies, each 35 days in length, were performed to investigate the relationship between tryptophan intake and the proportion of dietary tryptophan converted to niacin and the effect of supplements of L-leucine and vitamin B6 on this conversion. Nine college men consumed a basal diet that provided 8 mg of niacin, 1 mg of vitamin B6, and either 245, 548, or 845 mg of tryptophan from proteins per day. During each 35-day study, for one 15-day period basal diet alone was consumed, for another 15-day period basal diet plus 10 g of L-leucine per day was consumed, and for the last 5-day period, 20 mg of vitamin B6 per day was added to the diets of both groups. N1-methylnicotinamide, N1-methyl-2-pyridone-5-carboxamide, and quinolinic acid were measured in 24-hr urine samples. There were no significant or consistent effects of L-leucine or vitamin B6 supplements on the excretin of any of the metabolites measured. The proportion of tryptophan converted to niacin tended to increase as tryptophan consumption increased; however, this change was small and was probably not significant over the range of tryptophan intakes studied. The average conversion ration of tryptophan to niacin was approximately 72:1 in these subjects.

Choline/methionine nutrition of starting broiler chicks. Three models for estimating the choline requirement with economic considerations

Experiments were conducted to test the hypothesis that metabolically labile methyl groups and not methionine per se are limiting the growth of starting broiler chicks fed corn-soy-grease diets formulated to meet NRC (1977) recommendations (except for methionine). The basal diet contained approximately 23% protein, 3200 kcal ME/kg. 32% methionine, .42% cystine, and 1300 ppm choline. In the first two experiments the diets were fed to quadruplicate lots of 10 chicks in battery brooders. Average weight gain (g) and feed per unit gain for supplements of methyl group sources were: 1) methionine: 424, 1.48; 2) choline Cl: 406, 1.49; and 3) betaine HCl: 416, 1.48. These values were not significantly different from one another (P greater than .05) but were significantly different (P less than .05) from the values for the basal (362, 1.57) and from the DL-homocystine supplemented groups (376, 1.56). This indicated that methyl group utilization was not impaired by a lack of the carbon skeleton of methionine. Five 3-week assays with five groups of 10 chicks per treatment (1050 chicks) were conducted to determine the choline requirement using the basal diet without supplemental methionine. Results from the five assays were pooled in computing regressions. Significant regressions (P less than .05) were found for broken-line linear (R2 = .630), quadratic (R2 = .556), and saturation kinetic (R2 = .642) models. The requirement was determined to approximately 2130 ppm by the broken-line linear model. The most economic feeding levels were estimated to be 4100 and 1910 ppm by the quadratic and saturation kinetic models, respectively. The economic implications of the three models are discussed.

Food and protein intake, glucagon, and distribution of alpha-aminoisobutyrate in the rat

Distribution of alpha-aminoisobutyric acid (AIB) in the rat was modified by food, dietary protein, and glucagon. In rats last fed 24 h before AIB injection, AIB clearance from plasma and uptake into liver were greater in rats fed a high-protein diet (60% casein) than in rats fed the control diet (18% casein); AIB clearance from plasma and uptake into muscle were lowered by a low-protein diet (6% casein). Feeding rats lowered clearance of AIB from plasma in low- and high-protein groups. Distribution ratios (AIB concentration in tissue water/AIB in plasma) were low in all tissues but liver during the first 7 h after feeding high protein when compared to the control values; ratios were low in muscle, heart, and kidney after feeding low protein. Maximum ratios occurred at different times for different tissues; the time was delayed by the high-protein diet in all tissues but liver. Glucagon increased all ratios in rats fed the control or low-protein diets, with the smallest changes occurring in liver and muscle from low-protein rats.

Effects of a low protein diet during pregnancy of the rhesus monkey. III. Growth of infants

The growth of eight infants born to pregnant rhesus monkeys fed a control diet of modified cows' milk was compared to the growth of five infants born to mothers fed a diet containing only 25% as much protein but made isocaloric with supplemental lactose. The average body weight of infants whose mothers were fed the low protein diet was significantly less at birth and on day 180 after birth than for the infants whose mothers were fed the control diet. The mean head circumference was significantly less for the prenatally malnourished infants than for the control infants at birth; at day 180 after birth there was no significant difference. Although the average body length of infants from mothers fed the low protein diet was consistently less than that of infants from mothers fed the control diet, the differences were not significant.

Sulfur amino acid and methyl donor status of corn-soy diets fed to starting broiler chicks and turkey poults

Experiments were conducted to determine the effects of supplementing corn-soy-bean meal-white grease diets with sulfur amino acids and methyl group donors for starting broiler-strain chicks. The diets (23% protein and 3200 kcal ME/kg) were fed to quadruplicate lots of chicks in battery brooders. The diets were calculated to contain .37% methionine, .37% cystine, and 1499 mg/kg choline. Chemical and microbiological assays yielded values of .32% and .42% for methionine and cystine content respectively. Results of 5 chick experiments showed that supplementing this diet with .23% DL-methionine significantly (P less than .05) improved 3 week-gain (375 vs. 415 g) and feed/gain (1.54 vs. 1.47) over that obtained with the basal diet. When L-cystine and 2(CaSO4).H2O failed to give a significant (P greater than .05) response, compounds capable of donating methyl groups were fed. Significant (P less than .05) responses in gain (404 and 420) and feed/gain (1.48 and 1.51) over the basal were obtained with choline and betaine. These responses were not significantly (P greater than .05) different from that obtained with methionine. Serine and sodium formate failed to give consistent responses. Using a poult diet of 28% protein and 2800 kcal ME/kg, a significant (P less than .05) response to DL-methionine was again observed, with intermediate responses to betaine, choline, and serine. It is concluded that (within the limits of the experimental model) corn-soy type diets contain an adequate amount of total sulfur amino acid for chicks, but not poults, when sufficient choline or betaine are provided.

Induction of threonine imbalance by dispensable amino acids: relation to competition for amino acid transport into brain

The ability of low protein diets containing small neutral, dispensable amino acids to induce threonine imbalance has been examined. Diets containing amino acids which compete for threonine transport in vitro (serine, alanine, alpha-amino-n-butyrate) caused depressions of growth and food intake which could be corrected to varying degrees by adding threonine to the diet. Large neutral, indispensable amino acids, moderately inhibitory of threonine transport, also induced the imbalance. Some amino acids that had little or no effect on threonine transport in vitro (acidic amino acids and proline) did not cause growth and food intake depressions. Other non-inhibitory amino acids (arginine and lysine) caused growth depressions which were not satisfactorily corrected by additional threonine alone, but were prevented by supplements of all the indispensable amino acids including threonine. Ornithine which was also not inhibitory of threonine transport was an exception. It induced a moderate growth depression which was corrected by additional threonine. Similar studies showed that histidine or tryptophan imbalance could be induced by feeding diets containing only those large neutral amino acids which compete for histidine or tryptophan transport in vitro. These experiments show that, based on the results of transport competition experiments, it is generally possible to devise amino acid supplements which can induce a dietary imbalance of a given amino acid.

Metabolism and transport of gamma-carboxyglutamic acid

gamma-Carboxyglutamic acid residues have beeh shown to be present in prothrombin, the other vitamin K-dependent clotting factors, and more recently in bone and kidney proteins. This amino acid is formed by a posttranslational vitamin K-dependent carboxylation of glutamyl residues in polypeptide precursors of these protens. It has now been demonstrated that this amino acid, either in the free or peptide-bound form, is not metabolically degraded by the rat, but is quantitatively excreted in the urine. In nephrectomized rats, the tissue concentration of intravenously administered gamma-carboxyglutamic acid is increased, but there is still no evidence of any oxidative metabolism of this amino acid. These amino acid is transported by kidney slices against a concentration gradient, but does not accumulate in liver, intestinal or brain tissues. Preliminary data suggest that gamma-carboxyglutamic acid may be concentrated by a carrier system different from that utilized by other amino acids.

Threonine metabolism in vivo: effect of threonine intake and prior induction of threonine dehydratase in rats

The metabolic fate of threonine was investigated in young male rats fed 15% amino acid diets containing from 0.15% to 0.85% of L-threonine. Liver serine-threonine dehydratase (S-TDH) activity did not increase with increasing dietary threonine content. The level of threonine required for maximum weight gain was not greater than 0.55% of the diet (or about 600 mumoles/day). Tissue free threonine content of rats fed the diets with 0.15% or 0.3% of threonine was very low but increased sharply with increasing dietary threonine content above 0.3%. During ad libitum feeding of these diets containing L-[U-14C]threonine, rate of oxidation of threonine was low when intake was in the range of the requirement for maximum growth, but increased, thereafter as threonine intake increased. A 30-fold induction of liver S-TDH, by prior feeding of an 80% casein diet, did not result in increased oxidation of threonine when dietary threonine content was 0.15%. When dietary threonine content was increased to 0.5%, oxidation of threonine increased slightly but significantly. With 3% of threonine in the diet, rats previously fed a 15% casein diet had extremely high tissue threonine concentrations whereas those with high S-TDH activity, due to the previous feeding of the 80% casein diet, oxidized threonine rapidly and tissue threonine concentrations were elevated much less.

Nutritional regulations and legislation--past developments, future implications

Laws to prohibit adulteration of foods were enacted before 1900, but the first steps in the development of nutritional regulations were taken only after passage of the Food, Drug and Cosmetic Act of 1938. This act authorized the Food and Drug Administration (FDA) to establish Standards of Identity for foods, including standards for enrichment with vitamins and minerals to meet Minimum Daily Requirements (MDRs). The legal definition of nutrients, however, has remained unclear. Vitamins are foods when used as supplements but drugs when prescribed as therapeutic agents. To protect consumers, in 1962 the FDA proposed Standards of Identity for Special Dietary Foods, e.g., vitamin supplements. Opposition to the proposal has been vigorous and was the subject of the longest hearings on record. Implementation of standards has been contested in the courts and curtailed by Congressional action. A bill passed in 1975 prohibits the FDA from establishing Standards of Identity for special dietary foods for adults. During the legal and political controversy, the validity of Recommended Dietary Allowances as nutritional standards was challenged but subsequently confirmed. Revised regulations for vitamin and mineral preparations, taking into account the Congressional and court actions, will become effective January 1, 1978, sixteen years after first being proposed.

Effects of branched-chain amino acid antagonism in the rat on tissue amino acid and keto acid concentrations

Growth rate, plasma amino acid, and alpha-keto acid concentrations and activities of the branched-chain amino acid degradative enzymes of rats were measured. Effects of ingestion of excessive amounts of branched-chain amino acids on these variables were determined. Excessive intake of a single branched-chain amino acid led rapidly to elevated plasma concentration of both the amino acid administered and its corresponding alpha-keto acid and, if the rats had previously been fed a low protein diet, to an increase in liver branched-chain alpha-keto acid dehydrogenase activity. Only leucine caused, in addition, marked growth and food intake depression and decreased plasma isoleucine, valine, alpha-keto-beta-methylvaleric acid and alpha-keto isovaleric acid concentrations. The growth depression was associated food intake depression and could be moderated by addition of isoleucine and valine to the diet. The decreases in plasma isoleucine, valine, alpha-keto-beta-methylvaleric acid and alpha-keto isovaleric acid were not caused by increased degradation of these metabolites to carbon dioxide as branched-chain amino acid oxidation rates in vivo were unchanged by leucine loading and the degradative enzymes were unchanged in adequately fed rats. The decreased concentrations of these amino and keto acids may be the result of decreased protein degradation or increased protein synthesis, possibly mediated by insulin.

Induction of pyridoxal phosphate-dependent enzymes in vitamin B-6 deficient rats

The effectiveness of dietary and hormonal treatments in inducing several pyridoxal phosphate-(PLP)-dependent enzymes has been examined in vitamin B-6 deficient rats. Holo- and apoenzymes of serine dehydratase and ornithine aminotransferase were inducible in both control and deficient rats by feeding them 80% casein diets or by injecting them with glucagon. Holo- and apotyrosine aminotransferase were induced in both control and deficient rats by injecting them with glucagon or with dexamethasone phosphate. Phosphoenolpyruvate carboxykinase, a non-PLP-dependent enzyme, was inducible in both control and deficient rats by glucagon treatment if the rats were fed, but not if they had been starved. The degree of induction of certain enzymes depended upon whether rats were fed ad libitum, starved overnight, or fed a protein-free diet prior to the induction period. Phosphoenolpyruvate carboxykinase activities were about the same in both control and deficient rats. In vitamin B-6 deficient rats, both uninduced and induced activities of serine dehydratase, ornithine aminotransferase, and tyrosine aminotransferase assayed in the prsence of PLP, but not in its absence, either equaled or exceeded control values under most experimental conditions. Synthesis of excess of apoenzyme of PLP-dependent enzymes generally accounted for the high total enzyme activity in deficient rats. Differences between values for control and deficient rats could not be accounted for by differences in liver cyclic AMP concentrations nor were they apparently related to reduced food intake of the deficient rats. High apoenzyme concentration during depletion of coenzyme would tend to prevent depletion of active enzyme.

alpha-Aminoisobutyric acid transport in liver slices from rats fed low protein meals

The effect of low protein intake on alpha-aminioisobutyric acid (AIB) transport has been examined in liver slices from meal-fed rats. Treatments (force-feeding casein or gelatin hydrolysates, glycine, or potassium chloride; injecting glucagon, or preincubating liver slices with cyclic AMP) which stimulated transport in control rat fed 3-hour meals containing 18% casein were less effective in rats fed 6% casein meals for 8 days. Responses of protein-depleted rats to glucagon or cyclic AMP had become essentially normal after they had consumed 18% casein meals for 2 days, whereas between 6 to 10 days were required for complete recovery of the response to casein hydrolysate. Stimulation of AIB transport by casein hydrolysate was also normal in depleted rats after they had consumed 40% casein meals for 2 days. Basal, non-stimulated transport of AIB was not significantly depressed in rats fed the low protein diet. Casein hydrolysate-induced increases in hepatic cyclic AMP concentrations were smaller in rats fed low protein meals. The results show that, although various stimuli of hepatic AIB transport become less effective in the protein-deprived rat, relatively rapid recovery of the response can occur upon refeeding adequate or high levels of protein.

Conditions affecting plasma amino acid patterns in chickens fed practical and purified diets

Experiments were conducted to investigate plasma free amino acid concentrations in the chick. After one hour of fasting, total plasma amino acid concentration decreased to approximately half of the full-fed value. Within three to six hours, most amino acids had returned toward the full-fed level but did not exceed it throughout a 48 hour period of starvation. However, after 48 hours fasting lysine, threonine, and isoleucine accumulated three-fold, two-fold and two-fold of the full-fed level, respectively. Serine and glutamic acid exceeded the full-fed level at three hours and then declined. Alanine reached its highest level after six hours of fasting and then declined. In full-fed chicks diurnal variations of plasma free amino acid concentrations were observed. The lowest and highest concentrations were observed at 11 a.m. and 8 to 11 p.m., respectively under a 24 hr-lighting. Reference plasma amino acid patterns are reported for chicks fed a practical diet ad libitum. In day-old chicks, concentrations of total amino acids, methionine plus one half cystine, lysine, and arginine were high. Alanine and glutamic acid concentrations were low. Most amino acid concentrations declined gradually during the first four weeks of life, but methionine plus one half cystine, phenylalaine, threonine and serine concentrations decreased sharply between two and four weeks. Lysine concentration continued to decrease in chicks fed the starter diet. At 20 weeks, plasma amino acid concentrations had decreased considerably except for methionine plus one half cystine and basic amino acids. The plasma amino acid pattern for chicks fed an isolated soybean protein diet was similar to that of chicks fed the practical diet.

Studies on the production and assessment of experimental histidinemia in the rat

Intraperitoneal administration to rats of D- or DL-alpha-hydrazinoimidazolylpropionic acid was found to produce a substantial inactivation of hepatic histidine ammonia-lyase (EC 4.3.1.3) in vivo. Proportional to this loss in enzyme activity was an impairment of the ability of treated rats to oxidize L-[ring-2-14C] histidine to 14CO2. Rats in which hepatic histidine ammonia-lyase activity was either depressed by DL-hydrazinoimidazolylproprionic acid injection or elevated by feeding a high protein diet displayed proportionately altered rates of 3H2O release into plasma water following L-[3-3H] histidine administration. Plasma L-histidine clearance following loading with this amino acid was similarly affected by these treatments. Administration of DL-alphal-hydrazinoimisazolylproprionic acid to rats was also found to inactivate non-specifically pyridoxal 5-phosphate enzymes in vivo; pyridoxine injection was found to reverse the DL-alpha-hydrazinoimidazolylproprionic acid-induced inactivation of hepatic aspartate aminotransferase (EC 2.6.1.1) in vivo, but not that of hepatic histidine ammonia-lyase. These findings demonstrate that histidine ammonia-lyase is the rate-limiting factor in L-histidine degradation in the rat. The potential usefulness of DL-hydrazinoimidazolylproprionic acid in the production of an animal model for histidinemia (hereditary histidine ammonia-lyase deficiency) is discussed.

Branched-chain amino acid oxidation by isolated rat tissue preparations

Branched-chain amino acid transaminase activity, branced-chain alpha-keto acid dehydrogenase activity, and leucine oxidation were measured in homogenates and slices of several rat tissues. Transaminase activity was highest in heart, while dehydrogenase activity was highest in liver. Leucine oxidation in isolated tissues may be limited by either transaminase or dehydrogenase activity depending upon the relative activities of these two enzymes in the tissue. The results suggest that, as the load of branched-chain amino acids increases, the liver may become an increasingly important site for the degradation of branched-chain alpha-keto acids.

Significance of choline synthesis in the oxidation of the methionine methyl group in rats

Experiments were conducted to assess the significance of de novo choline synthesis in the oxidative metabolism of the methyl group of L-methionine in the rat. Comparison of the rates of 14CO2 production by rats fed diets containing equimolar or equal methyl loads of [methyl-14C]methionine, [methyl-14C] choline, [methyl-14C] betaine and [methyl-14C] sarcosine revealed that the methyl groups of choline, betaine and sarcosine were oxidized at rates nearly equivalent to or exceeding that of the methionine methyl group. However, the results of a second series of in vivo experiments using non-radioactive choline or betaine as intermediary trapping pools indicated that little newly formed radioactive choline was released from tissue phospholipid choline during the period of rapid 14CO2 production from [14CH3] methionine. Incorporation of the methionine methyl group into phospholipid choline by incubated liver slices was strongly inhibited by 2-methoxyethanol without a parallel inhibition of methionine methyl group oxidation. Results of these in vitro studies also indicated that the metabolic pathway responsible for the transfer of the methionine methyl group into choline and that responsible for its oxidation to CO2 differ widely in the ease with which they can be saturated by L-methionine. It is concluded that essentially all of the methionine methyl group oxidation in vitro and that occurring during the absorptive period in vivo must depend primarily on pathways other than those leading to the synthesis of choline.

Histidine ammonia-lyase from rat liver. Purification, properties, and inhibition by substrate analogues

Histidine ammonia-lyase (EC 4.3.1.3) from rat liver was purified more than 250-fold to near homogeneity. Electrophoretic determinations indicated a native molecular weight of approximately 200,000. The enzyme has a pH optimum of approximately pH 8.5. The minimum Km for L-histidine was 0.5 mM at pH 9.0. The Michaelis constant in the physiological pH range was, however, more than 2.0 mM. D-alpha-hydrazinoimidazolylpropionic acid was found to be a potent competitive inhibitor of liver histidine ammonia-lyase (Kis=75 muM); the L enantiomer of this compound was less effective in this regard. The enzyme was also inhibited competitively by L-histidine hydroxamate (Kis=0.4 mM), and to a lesser extent by L-histidinol, D-histidine, and glycine. Failure of a wide variety of other histidine analogues to inhibit the enzyme substantially indicates high specificity of the active site for L-histidine. No alternate substrates were identified for the enzyme. DL-alpha-Hydrazinophenylpropionic acid, the alpha-hydrzino analogue of phenylalanine, was similarly shown to be a very potent competitive inhibitor of a mechanistically similar L-phenylalanine ammonia-lyase purified from Rhodotorula glutinis. The properties of histidine ammonia-lyase from rat liver differ significantly from those of the enzyme from Pseudomonas fluorescens which has been studied most extensively to date.

Stability of some pyridoxal phosphate-dependent enzymes in vitamin B-6 deficient rats

The effects of lowering the liver pyridoxal phosphate (PLP) concentration by vitamin B-6 deficiency on the stability of several rat liver enzymes were examined. Three PLP-dependent enzymes (serine dehydratase, ornithine-delta-aminotransferase, and tyrosine aminotransferase) and two non-PLP-dependent enzymes (glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxykinase) were induced in vitamin B-6 deficient and control rats by feeding them high-protein diets or by injecting them with glucagon or dexamethasone. The decline of each activity was followed after withdrawal of the inducer. Serine dehydratase activity declined more rapidly in vitamin B-6 deficient than in control liver; however, ornithine aminotransferase and tyrosine aminotransferase activities were equally stable in deficient and control liver. Ornithine aminotransferase was predominantly in holoenzyme form in both control and deficient rats, whereas tyrosine aminotransferase was predominantly in apoenzyme form in both groups. The proportion of serine dehydratase in apoenzyme was less stable than the holoenzyme. Activity changes of glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxykinase in control and vitamin B-6 deficient rats were similar. The results suggest that differences in the stability of PLP-dependent enzymes in vitamin B-6 deficient rats depend upon differences in the proportions of these enzymes existing as holo- and apoenzyme.

Effects of a low-protein diet during pregnancy of the rhesus monkey I. Reproductive efficiency

Pregnant rhesus monkeys were fed a control diet of modified cow's milk or an experimental diet containing only 25% as much as protein but made isocaloric with supplemental lactose. The ad libitum consumption of the control and experimental diets provided about 2 and 0.5 g of protein/kg of body weight per day, respectively. Total volume and energy consumption of control and experimental animals were generally comparable per kilogram of body weight, with groups showing a reduction in intake of about 20% during the latter part of pregnancy. Control females gained an average of 1.3 kg during pregnancy compared to 0.02 kg by the monkeys fed the low-protein diet. One of 15 infants born to control animals died shortly after birth; eight of 16 pregnancies in animals on the low-protein diet resulted in maternal and fetal death, stillbirth, or death in the newborn period. The birth weight of full term infants from mothers fed the low-protein diet was depressed by about 15%, and fetal linear growth was affected very little, but fetal and perinatal survival were low. We conclude that growth measurements of the newborn infants were relatively insensitive indices of the severity of the maternal nutritional deficiency and of the prognosis for the infant.

Is L-glutamic acid nutritionally a dispensable amino acid for the young chick?

The importance of dispensable amino acids for the chick was reinvestigated. Two-week chick weights were 75.7 g. and 143.7 g. when dietary nitrogen was provided solely by indispensable amino acids and by indispensable amino acids and 10% L-glutamic acid, respectively. Weight gain increased four-fold when L-glutamic acid was added to the mixture of indispensable amino acids. Plasma free amino acid concentrations were considerably decreased and total indispensable amino acid concentration (including cystine and tyrosine) was reduced to approximately a half or less with L-glutamic acid supplementation. Increments of L-glutamic acid as the sole nitrogen source for dispensable amino acids in the diet increased two-week weight gain proportionately over a range from 0 to 10%. When 10% of L-glutamic acid was included in the amino acid diet, growth rate was equivalent to that with a practical diet up to two weeks of age. The mixture of leucine, isoleucine, valine, lysine and arginine produced little growth promotion as a nitrogen source for dispensable amino acids. L-aspartic acid, L-alanine and the mixture of dispensable amino acids devoid of L-glutamic acid were found not as effective as L-glutamic acid. The estimate of effectiveness of L-aspartic acid, L-alanine and the mixture was approximately 80%, 60%, and 80%, respectively, of that of L-glutamic acid during first two weeks. Utilization of diammonium citrate for growth promotion varied with the amount used and the age of chicks. A combination of dispensable amino acids plus nominal levels of DAC was not as effective as glutamic acid during the first week but shortly after that, produced good gains. Even during the 3rd week or 4th week high levels of DAC alone did not produce normal gains of chicks. The activities and the subcellular distribution of glutamic pyruvic transaminase (GPT) and glutamic oxaloacetic transaminase (GOT) in the liver of young chicks were measured. GOT activity was considerably higher than GPT activity. Initially, GOT activity was found primarily in cytosol, but the mitochondrial activity increased to 57% of total activity by day 10, whereas GPT activity was exclusively in mitochondria regardless of the age.

Effects of D-, DL-and L-glutamic acid on chicks

Studies were conducted to investigate the effects of D-, DL-, or L-glutamic acid on the chick. Supplementation of levels of L-glutamic acid to an amino acid mixture containing adequate levels of all the indispensable amino acids plus cystine and tyrosine resulted in increased growth up to 10% L-glutamic acid in the diet. Chicks tolerated as much as 15% L-glutamic acid with no growth retardation. Supplementation of D-glutamic acid at levels of 3.75 or 5% resulted in growth depressions of 18 and 38%, respectively, at the end of a 2-week experiment. Significant growth-depressing effects of these levels of D-glutamic acid and 7.5% of DL-glutamic acid were also observed with an amino acid diet as well as an isolated soybean protein diet. The growth-depressing effect was most severe during week 2 of the experiment. Additional vitamins and amino acid supplements failed to reverse the growth-depressing effect. Plasma glutamic acid concentration was not altered by the inclusion of D-glutamic acid in the diet, but generally, plasma free amino acid concentrations were increased. This was especially true of arginine. Free glutamic acid increased in the kidney and was lowered in the liver. Free ammonia was increased in both the liver and kidney when the D form was included in the diet. Implications of these findings are discussed.

An evaluation of the nutritive value of new high protein oat varieties (cultivars)

Studies were conducted to evaluate the nutritive value of new high protein oat varieties using chicks and rats. Oat groats studied were Lodi, Dal, and Goodland; protein contents were 16.0, 18.0, and 20.5%, respectively. Increases in protein content were accompanied with an increase in indispensable amino acids. The lysine contents of Lodi and Goodland oat groats were 0.60 and 0.72%, respectively. With amino acid supplementation the 80% oat groats diets supported a growth rate of chicks comparable with that of a practical diet for up to 2 weeks. To correct amino acid deficiency, Goodland, Dal, and Lodi oat groats diets were supplemented with 0.55, 0.60, and 0.65% lysine and 3.2, 5.1, and 6.6% of a mixture of other amino acids. Omission of lysine from the amino acid supplement resulted in retarded growth and marked reduction of plasma free lysine concentration. For Goodland oat groats, the chemical score was 51. Protein efficiency ratio with rats was 2.2, which was increased to 2.4 by lysine and methionine supplementation, while protein efficiency ratio for whole egg protein was 3.4. The slope-ratio assay rendered a relative nutritive value of 59 for Goodland oat groats, assuming 100 for whole egg protein. This value was increased to 67 by lysine and methionine supplementation.

Effect of maternal protein deprivation on enzymatic development in newborn rats

Postnatal development of liver tyrosine aminotransferase and glucose-6-phosphatase, expressed as activity per gram of liver, occurred as rapidly in pups from pregnant rats fed throughout gestation a diet containing only 4% of casein as in pups from those fed the control diet containing 18% of casein supplemented with 0.3% of L-methionine. Total enzyme activity per liver was lower in pups from protein-restricted dams due to their smaller liver size. Dams fed the 4% casein diet during pregnancy gained much less weight than those fed the control diet and produced pups that weighed significantly less than control pups. Reproductive performance of a few dams fed 6% casein diets with or without amino acid supplements during gestation was comparable to that of dams fed the control diet. Litter size was not significantly reduced by the low-protein intake.

Protein synthesis in liver, muscle, and brain of rats fed a high tyrosine-low protein diet

Effects of feeding rats a high tyrosine-low protein diet on protein synthesis in liver, muscle, and brain were investigated both in vitro and in vivo. Tissue tyrosine concentrations of rats consuming the high tyrosine diet for 7 days were substantially elevated; this was accompanied by severe growth retardation. In the livers of rats fed the high tyrosine diet for 6 days, polysomal profiles showed a shift toward heavier ribosomal aggregates, while in muscle and brain, extensive disaggregation of polysomes occurred. In an in vitro amino acid incorporating system, the activities of both the microsomal and pH 5 enzyme fractions isolated from the livers of the high tyrosine animals that had been fed the diet for 6 weeks were elevated. On the other hand, the capacity of muscle or brain ribosomal preparations to incorporate [14-C] leucine was much reduced. Similar results were obtained in a study of [14-C] leucine incorporation in vivo in which rats were force-fed two meals and killed at various times after the last feeding. In rats fed the high tyrosine diet, incorporation of leucine into liver increased progressively; this was accompanied by a gradual decrease in leucine incorporation into muscle. In contrast, leucine incorporation into brain was immediately suppressed. In view of the apparently paradoxical effect of a high tyrosine load on protein synthesis in the liver, rates of the anabolic and catabolic phases of protein turnover in animals fed a high tyrosine diet were determined from radioactivity measurements made after pulse labeling them with [14-C] bicarbonate. Results indicated that the rates of both synthesis and degradation of liver proteins were elevated over control values. Differences in the effects of a toxic load of tyrosine on protein synthesis in the tissues examined could be the consequence of altered metabolic or hormonal balance as a result of nutritional stress.