Source Of Leucine Research Articles

Amino acid composition of canned main dish increased food value

It is relevant to reduce the meat raw material in the composition of canned main dishes – porridge with meat due to the unsatisfactory state of livestock production in Ukraine. It is promising to use in the technology of canned main dishes – porridge with meat of non-traditional cereals – spelt, which is superior in terms of amino acid composition to certain types of traditionally used cereals. The purpose of the article is to study the amino acid composition of the canned main dish – porridge with meat containing spelt groats. The mass fraction of essential amino acids was determined by the chromatographic method. The amino acid score, the coefficient of its discrepancy and the biological value determined by calculation method. According to the results of determining the content of essential amino acids in porridge with meat containing spelt groats (experimental sample), their amount was lower compared to the control, namely isoleucine – by 44.74 %, lysine – by 23.75 %, leucine – by 14.64 %, threonine – by 11.36 %, valine – by 9.26 %, methionine – by 12.00 %, tryptophan – by 7.69 %, phenylalanine – by 2.17 %, histidine – by 8.57 %. The developed canned main dish – porridge with meat containing spelt groats is a source of leucine and lysine. The calculation of the amino acid score in experimental sample showed that all essential amino acids have a value of 100 % and above, and the limited amino acid is isoleucine, the score of which is 100 %, and the highest score belongs to histidine – 181 %. It was established that the coefficient of divergence of the amino acid score in experimental sample is higher by 2.56 %, and the indicator of biological value is lower by 2.57 % compared to the control, which is not significant. Thus, the reduction of meat raw materials in the recipe composition of porridge with meat made it possible to preserve the amino acid composition due to the use of spelt groats, and the finished product can be classified as a complete food product.

Lifetime correction of quality indicators of pork

For the first time, the composition of a feed additive from modern biologically active substances and natural components with a synergistic effect has been scientifically substantiated, which is capable of forming biologically complete, environmentally friendly products in animals at the final stage of growing (a month before slaughter). This additive consists of,%: 95.5 – micronized full fat soya (source of leucine – controller of adipopexis), 3.5 – betaine (osmoprotection moisture retention in muscle tissue), 0.3 – L-carnitine (an activator of energy metabolism), 0.7 – Lisofort (emulsifier of fats, improving its digestion). It was found that the use of a functional feed additive in the amount of 2.0% 30 days before slaughter of pigs increases its productivity by 9.3%, reduces feed costs for products by 8.4%. In muscle tissue, fat content increased by 0.85 %, characterizing the improvement of “marbling” of meat. The moisture-binding ability increased by 8.0%, the color intensity by 5.0 units of extinction, and a protein-quality indicator of meat due to an increase of 4.68% in the content of essential amino acids. The economic efficiency of the use of functional feed additives for the final fattening of pigs was calculated.

Plasma Amino Acid Concentrations After the Ingestion of Dairy and Collagen Proteins, in Healthy Active Males.

Introduction: Recent evidence suggests that the consumption of essential amino acids (AA) and/or those abundantly present in collagen may have the capacity to influence the synthesis of new collagen in ligaments and tendons, when tissue perfusion is optimized (e.g., during exercise). However, little is currently known about the bioavailability of these AAs in blood after the consumption of various collagen and diary protein sources: such information is needed to develop potentially useful dietary and supplement intake strategies.Objectives: The aim of the current study was to characterize blood AA concentrations in response to consumption of collagen and dairy protein sources; specifically, maximum concentrations, the timing of maximum concentration, and total (area under the curve) exposure above baseline.Methods: A 20 g serve of various dairy and collagen proteins, and a 300 mL serve of bone broth were consumed by healthy, recreationally active males after an overnight fast. Blood samples were drawn every 20 min for a total of 180 min, for analysis of plasma AA concentrations. Total AA, essential AA and collagen specific AAs were analyzed for maximum concentration, timing of peak, and area under the curve.Results: In general, protein intake was associated with a similar increase in total and collagen specific AAs, except for collagen proteins being a superior source of glycine (683 ± 166 μmol/L) compared to 260 ± 65 μmol/L for dairy proteins (P < 0.0001), whilst dairy proteins were a superior source of leucine (267 ± 77 μmol/L) compared to 189 ± μmol/L for collagen proteins (P < 0.04). Although there were several differences in the bioavailability of hydrolysed compared to non-hydrolysed proteins, this only reached statistical significance within the dairy proteins, but not for collagen proteins.Conclusions: The intake of collagen proteins result in higher plasma peaks of glycine, whilst the intake of dairy proteins result in higher plasma peaks of leucine. This information may support further investigations, and identification of key AAs that may support exercise in the synthesis of collagen.

Egg Intake in Chronic Kidney Disease.

Patients with chronic kidney disease (CKD) are often instructed to adhere to a renal-specific diet depending on the severity and stage of their kidney disease. The prescribed diet may limit certain nutrients, such as phosphorus and potassium, or encourage the consumption of others, such as high biological value (HBV) proteins. Eggs are an inexpensive, easily available and high-quality source of protein, as well as a rich source of leucine, an essential amino acid that plays a role in muscle protein synthesis. However, egg yolk is a concentrated source of both phosphorus and the trimethylamine N-oxide precursor, choline, both of which may have potentially harmful effects in CKD. The yolk is also an abundant source of cholesterol which has been extensively studied for its effects on lipoprotein cholesterol and the risk of cardiovascular disease. Efforts to reduce dietary cholesterol to manage dyslipidemia in dialysis patients (already following a renal diet) have not been shown to offer additional benefit. There is a paucity of data regarding the impact of egg consumption on lipid profiles of CKD patients. Additionally, egg consumption has not been associated with the risk of developing CKD based on epidemiological studies. The egg yolk also contains bioactive compounds, including lutein, zeaxanthin, and vitamin D, which may confer health benefits in CKD patients. Here we review research on egg intake and CKD, discuss both potential contraindications and favorable effects of egg consumption, and describe the need for further research examining egg intake and outcomes in the CKD and end-stage renal disease population.

Prospects for the use of alfalfa seeds in the production of special food products

The article is devoted to the problem of protein nutrition deficiency among the planet's population. The urgency of attracting protein-containing vegetable crops to diets of various groups of the population is revealed. It is noted that in recent years, the population has seen a decrease in the intake of complex carbohydrates, an increase in the intake of easily digestible carbohydrate and fatty foods. The consequence of an unbalanced diet is a decrease in life expectancy, an increase in endocrine and cardiovascular diseases. It is found out that alfalfa is a domestic unpretentious agricultural crop with a high yield and is widely cultivated in Russia. It is found out that alfalfa is a domestic unpretentious agricultural crop with a high yield and is widely cultivated in Russia. The prospect of attracting alfalfa to food production has been established. The chemical composition of the seeds of alfalfa has been studied. The article presents the results of studies to determine the content of vitamins, the composition of amino acids, the amount of macro- and microelements in the object. It was found out that the chemical composition of alfalfa seeds is characterized by a high content of protein, complex carbohydrates, fiber, vitamins (A, B3, B5, B9, E, K), macro- (potassium, calcium, magnesium, sodium, phosphorus) and microelements (iron, manganese, copper, zinc). Lucerne can be an effective source of leucine, lysine, isoleucine, valine and threonine. Based on the above studies, it is concluded that the seeds of alfalfa are a promising raw material for the replacement of animal proteins, the enrichment of low nutritional vegetable proteins, the regulation of the chemical composition of catering products, the creation of analogues of food products and the development of specialized products of baby food. Alfalfa seeds are proposed for the development of low-calorie food formulas, food products with low cholesterol and the creation of specialized products for the correction of metabolic disorders of the body. It is shown that alfalfa, along with other domestic agricultural crops, is very promising in food production.

A native whey protein extract

Nutritional recommendations for the prevention and management of sarcopenia, now defined as a loss of muscle mass and muscle function (strength or performance), has recently been established by expert panels (see Appendix 1 for the prevalence of sarcopenia). It appears that exercise with adequate leucine-rich protein supplementation is necessary to preserve muscle function during ageing. The main commercially available protein source of leucine are native whey proteins directly extracted from milk. Clinical studies performed with native whey proteins* (NWP) have shown that a daily moderate consumption of NWP promoted an increase in postprandial protein anabolism and resistance to fatigue in elderly persons by improving the effect of exercise on muscle function.

Egg Protein as a Source of Power, Strength, and Energy

In Brief High-quality proteins make a valuable contribution to the synthesis and maintenance of muscle and indirectly to the regulation of blood glucose levels, thus contributing to power, strength, and energy. Eggs have traditionally been used as the standard of comparison for measuring protein quality because of their essential amino acid (EAA) profile and high digestibility. They provide a nutrient-dense source of energy from protein and fat, approximately 75 kcal per large egg, as well as several B vitamins, including thiamin, riboflavin, folate, B12, and B6, which are required for the production of energy by the body. Given the unique complementary relationship between the EAA leucine and glucose utilization by muscle, it would follow that a diet rich in the amino acid leucine would be advantageous to men and women undergoing endurance training. Leucine is also a critical element in regulating muscle protein synthesis and may be the key amino acid defining the increased needs for EAA to optimize skeletal muscle mass. Increased tissue levels of leucine combine with circulating insulin to allow skeletal muscles to manage protein metabolism and fuel selection in relation to diet composition. Moreover, muscle recovery from exercise, both resistance and endurance, seems to be dependent on dietary leucine. Because eggs are an excellent, nutrient-rich source of leucine, as well as other EAAs, these protein-related benefits may be important to active individuals who routinely consume eggs as part of a varied, balanced diet Do eggs deserve a second look?

A highly active adipyl‐cephalosporin acylase obtained via rational randomization

There is strong interest in creating an enzyme that can deacylate natural cephalosporins such as cephalosporin C in order to efficiently acquire the starting compound for the industrial production of semisynthetic cephalosporin antibiotics. In this study, the active site of the glutaryl acylase from Pseudomonas SY-77 was randomized rationally. Several mutations that were found in previous studies to enhance the activity of the enzyme towards adipyl-7-aminodesacetoxycephalosporanic acid (ADCA) and cephalosporin C have now been combined, and libraries have been made in which random amino acid substitutions at these positions are joined. The mutants were expressed in a leucine-deficient Escherichia coli strain and subjected to growth selection with adipyl-leucine or amino-adipyl-leucine as sole leucine source. The mutants growing on these media were selected and purified, and their hydrolysis activities towards adipyl-7-ADCA and cephalosporin C were tested. Several mutants with highly improved activities towards the desired substrates were found in these rationally randomized libraries. The best mutant was selected from a library of totally randomized residues: 178, 266, and 375. This mutant comprises two mutations, Y178F + F375H, which synergistically improve the catalytic efficiency towards adipyl-7-ADCA 36-fold. The activity of this mutant towards adipyl-7-ADCA is 50% of the activity of the wild-type enzyme towards the preferred substrate glutaryl-7-aminocephalosporanic acid, and therefore the characteristics of this mutant approach those needed for industrial application.

An integrative model of amino acid metabolism in the liver of the lactating dairy cow

The objective of this work was to construct a dynamic model of hepatic amino acid metabolism in the lactating dairy cow that could be parameterized using net flow data from in vivo experiments. The model considers 22 amino acids, ammonia, urea, and 13 energetic metabolites, and was parameterized using a steady-state balance model and two in vivo, net flow experiments conducted with mid-lactation dairy cows. Extracellular flows were derived directly from the observed data. An optimization routine was used to derive nine intracellular flows. The resulting dynamic model was found to be stable across a range of inputs suggesting that it can be perturbed and applied to other physiological states. Although nitrogen was generally in balance, leucine was in slight deficit compared to predicted needs for export protein synthesis, suggesting that an alternative source of leucine (e.g. peptides) was utilized. Simulations of varying glucagon concentrations indicated that an additional 5 mol/d of glucose could be synthesized at the reference substrate concentrations and blood flows. The increased glucose production was supported by increased removal from blood of lactate, glutamate, aspartate, alanine, asparagine, and glutamine. As glucose output increased, ketone body and acetate release increased while CO 2 release declined. The pattern of amino acids appearing in hepatic vein blood was affected by changes in amino acid concentration in portal vein blood, portal blood flow rate and glucagon concentration, with methionine and phenylalanine being the most affected of essential amino acids. Experimental evidence is insufficient to determine whether essential amino acids are affected by varying gluconeogenic demands.

DapE can function as an aspartyl peptidase in the presence of Mn2+.

Extracts of a multiply peptidase-deficient (pepNABDPQTE iadA iaaA) Salmonella enterica serovar Typhimurium strain contain an aspartyl dipeptidase activity that is dependent on Mn(2+). Purification of this activity followed by N-terminal sequencing of the protein suggested that the Mn(2+)-dependent peptidase is DapE (N-succinyl-L,L-diaminopimelate desuccinylase). A dapE chromosomal disruption was constructed and transduced into a multiply peptidase-deficient (MPD) strain. Crude extracts of this strain showed no aspartyl peptidase activity, and the strain failed to utilize Asp-Leu as a leucine source. The dapE gene was cloned into expression vectors in order to overproduce either the native protein (DapE) or a hexahistidine fusion protein (DapE-His(6)). Extracts of a strain carrying the plasmid overexpresssing native DapE in the MPD dapE background showed a 3,200-fold elevation of Mn(2+)-dependent aspartyl peptidase activity relative to the MPD dapE(+) strain. In addition, purified DapE-His(6) exhibited Mn(2+)-dependent peptidase activity toward aspartyl dipeptides. Growth of the MPD strain carrying a single genomic copy of dapE on Asp-Leu as a Leu source was slow but detectable. Overproduction of DapE in the MPD dapE strain allowed growth on Asp-Leu at a much faster rate. DapE was found to be specific for N-terminal aspartyl dipeptides: no N-terminal Glu, Met, or Leu peptides were hydrolyzed, nor were any peptides containing more than two amino acids. DapE is known to bind two divalent cations: one with high affinity and the other with lower affinity. Our data indicate that the form of DapE active as a peptidase contains Zn(2+) in the high-affinity site and Mn(2+) in the low-affinity site.

Altering the Substrate Specificity of Cephalosporin Acylase by Directed Evolution of the β-Subunit

Using directed evolution, we have selected an adipyl acylase enzyme that can be used for a one-step bioconversion of adipyl-7-aminodesacetoxycephalosporanic acid (adipyl-7-ADCA) to 7-ADCA, an important compound for the synthesis of semisynthetic cephalosporins. The starting point for the directed evolution was the glutaryl acylase from Pseudomonas SY-77. The gene fragment encoding the beta-subunit was divided into five overlapping parts that were mutagenized separately using error-prone PCR. Mutants were selected in a leucine-deficient host using adipyl-leucine as the sole leucine source. In total, 24 out of 41 plate-selected mutants were found to have a significantly improved ratio of adipyl-7-ADCA versus glutaryl-7-ACA hydrolysis. Several mutations around the substrate-binding site were isolated, especially in two hot spot positions: residues Phe-375 and Asn-266. Five mutants were further characterized by determination of their Michaelis-Menten parameters. Strikingly, mutant SY-77(N266H) shows a nearly 10-fold improved catalytic efficiency (k(cat)/K(m)) on adipyl-7-ADCA, resulting from a 50% increase in k(cat) and a 6-fold decrease in K(m), without decreasing the catalytic efficiency on glutaryl-7-ACA. In contrast, the improved adipyl/glutaryl activity ratio of mutant SY-77(F375L) mainly is a consequence of a decreased catalytic efficiency toward glutaryl-7-ACA. These results are discussed in the light of a structural model of SY-77 glutaryl acylase.

Aspartic peptide hydrolases in Salmonella enterica serovar typhimurium.

Two well-characterized enzymes in Salmonella enterica serovar Typhimurium and Escherichia coli are able to hydrolyze N-terminal aspartyl (Asp) dipeptides: peptidase B, a broad-specificity aminopeptidase, and peptidase E, an Asp-specific dipeptidase. A serovar Typhimurium strain lacking both of these enzymes, however, can still utilize most N-terminal Asp dipeptides as sources of amino acids, and extracts of such a strain contain additional enzymatic activities able to hydrolyze Asp dipeptides. Here we report two such activities from extracts of pepB pepE mutant strains of serovar Typhimurium identified by their ability to hydrolyze Asp-Leu. Although each of these activities hydrolyzes Asp-Leu at a measurable rate, the preferred substrates for both are N-terminal isoAsp peptides. One of the activities is a previously characterized isoAsp dipeptidase from E. coli, the product of the iadA gene. The other is the product of the serovar Typhimurium homolog of E. coli ybiK, a gene of previously unknown function. This gene product is a member of the N-terminal nucleophile structural family of amidohydrolases. Like most other members of this family, the mature enzyme is generated from a precursor protein by proteolytic cleavage and the active enzyme is a heterotetramer. Based on its ability to hydrolyze an N-terminal isoAsp tripeptide as well as isoAsp dipeptides, the enzyme appears to be an isoAsp aminopeptidase, and we propose that the gene encoding it be designated iaaA (isoAsp aminopeptidase). A strain lacking both IadA and IaaA in addition to peptidase B and peptidase E has been constructed. This strain utilizes Asp-Leu as a leucine source, and extracts of this strain contain at least one additional, as-yet-uncharacterized, peptidase able to cleave Asp dipeptides.

Stable Maintenance of Plasmid in Continuous Culture of Yeast under Non-Selective Conditions.

A recombinant yeast plasmid containing the gene for beta-galactosidase was tested for stability in a host auxotrophic for leucine. Plasmid loss was studied at different dilution rates in continuous culture under selective as well as non-selective conditions. It was observed that the instability of the culture was higher at low dilution rates in selective medium, while the pattern was reversed when complex non-selective medium was used, with plasmid-containing cells competing effectively with plasmid-free cells at low dilution rates. This was attributed to a low residual yeast extract concentration in the medium at low dilution rates. Since yeast extract was the sole source of leucine, this limited the growth of plasmid-free cells, which were auxotrophic for leucine. Growth rate studies also indicated a competitive advantage of the plasmid-containing cells over the plasmid-free cells at low yeast extract concentrations in semi-defined medium. Using the above data, a modified continuous culture was run using non-selective medium at a low dilution rate of 0.05 h(-1). This resulted in stable coexistence of plasmid-containing and plasmid-free cells and hence sustained expression of beta-galactosidase at approximately 330 OD420l(-1) h(-1) throughout the period of cultivation (134 h).

Stable maintenance of plasmid in continuous culture of yeast under non-selective conditions

A recombinant yeast plasmid containing the gene for β-galactosidase was tested for stability in a host auxotrophic for leucine. Plasmid loss was studied at different dilution rates in continuous culture under selective as well as non-selective conditions. It was observed that the instability of the culture was higher at low dilution rates in selective medium, while the pattern was reversed when complex non-selective medium was used, with plasmid-containing cells competing effectively with plasmid-free cells at low dilution rates. This was attributed to a low residual yeast extract concentration in the medium at low dilution rates. Since yeast extract was the sole source of leucine, this limited the growth of plasmid-free cells, which were auxotrophic for leucine. Growth rate studies also indicated a competitive advantage of the plasmid-containing cells over the plasmid-free cells at low yeast extract concentrations in semi-defined medium. Using the above data, a modified continuous culture was run using non-selective medium at a low dilution rate of 0.05 h −1. This resulted in stable coexistence of plasmid-containing and plasmid-free cells and hence sustained expression of β-galactosidase at ∼330 OD 420 l −1 h −1 throughout the period of cultivation (134 h).

Leucine transport from mother to fetus in rat: Role of the visceral yolk sac

It is known that intracellular proteolysis of exogenous protein in the visceral yolk sac (VYS) is a significant source of leucine for the fetus from days 8.5 through 17.5 post-conception in the rat. In contrast, little attention has been paid to the potential of the VYS to transport maternal free amino acids to the fetus. We investigated this question using the exteriorized 17.5-day rat fetus, enclosed within its amnion and VYS, but with its placenta attached to the uterus and still functional. We first demonstrated that [ 3H] leucine in medium bathing the exteriorized fetus is transported by the VYS to the fetus and then exchanged with the leucine pool in the maternal circulation. This result indicates that the preparation remains viable for the duration of the experiment. We next injected a trace amount of [ 3H] leucine intravenously into the 17.5-day pregnant rat and found that the concentration of radioactivity in the plasma of the exteriorized fetus was not much lower than that in plasma of non-exteriorized fetuses in the same litter (8–15 fetuses per litter). We interpret these results to indicate that the VYS transports free leucine to the fetus but that this process makes a minor contribution to the total transfer of free leucine into the 17.5-day rat fetus.

Leucine Transport through Cation Exchange Membranes: Effects of HCl Concentration on Interfacial Transport

The leucine permeability coefficients,P, through a cation exchange membrane were measured as a function of HCl concentration,CHCl, from 0 to 10−1mol/L for three different interfacial conditions and were compared with the results for glycine. Leucine transport phenomena remarkably depended on the interfacial condition between the membrane and the external solution. The lowestP(2.33 × 10−8cm2/s) was obtained atCHCl= 0 for both sides of the membrane, and generallyPincreases with an increase inCHCl. In case of the glycine, the lowestP(1.85 × 10−7cm2/s) had been obtained ifCHClon the glycine source side was 10−1mol/L and that on the opposite side was 0. The highestP(4.34 × 10−7cm2/s) was obtained ifCHClon the leucine source side was 0 and that on the opposite side was 10−1mol/L as well as for glycine (4.16 × 10−6cm2/s). ThePvalues of glycine had been explained by the transport mechanism based on the interfacial chemical reaction (protonation, deprotonation, or ion-exchange) and the ionic transport across a charged membrane. ThePvalues of leucine were also explained qualitatively by the same mechanism as glycine; however, they are remakably affected by the physicochemical properties of the membrane, such as hydrophobicity and molecular size.

Leucine sources for 10.5-day rat conceptus in vivo

Protein has been shown to be the principal source of leucine for the Day 8.5 to 10.5 rat conceptus in culture. It could be argued that this finding applies only after adaptation to culture conditions and does not apply in vivo. This possibility was investigated using an isotope-dilution technique after I.V. injection of [ 3H]leucine into Day 10.5 pregnant rats. Specific radioactivity of free leucine in the conceptus was 8 to 10% of that in maternal plasma. Slow exchange of leucine with the maternal circulation and fetal tissue protein turnover were judged to be inadequate as explanations for the observed isotope dilution. Taken together, our results and those from in vitro studies are consistent with a major contribution of leucine coming from the degradation of protein in vivo, probably involving the visceral yolk sac. Our results suggest that mechanisms of amino acid supply to the conceptus identified using whole-embryo culture mirror those in vivo.

Isolation and mapping of a mutant penicillin G acylase with altered substrate specificity from Escherichia coli

Penicillin G acylase of Escherichia coli ATCC 11105 catalyzes hydrolysis as wellas synthesis of penicillin G. In this work a recombinant penicillin G acylase genewas mutagenized in vivo. A mutant with altered penicillin G acylase was selectedby its ability to grow with phthalyl-L-leucine as sole source of leucine. Themutant enzyme obtained was deficient in hydrolyzing penicillin G. A mutation ofGly359 to aspartic acid was mapped first by construction of chimeric pac genescomposed of wild type and mutant DNA, followed by nucleotide sequencing.

Carboxypeptidase yscS: gene structure and function of the vacuolar enzyme

The gene encoding carboxypeptidase yscS in Saccharomyces cerevisiae, CPS1, was cloned by complementation of the cps1-3 mutation. The cloned CPS1 gene, which again enabled a leucine auxotrophic cps1-3 mutant to grow on the modified dipeptide Cbz-Gly-Leu (Cbz, benzyloxycarbonyl) as sole leucine source, was sequenced and found to consist of an open reading frame of 1728 bp encoding a protein of 576 amino acids. The putative protein contains a hydrophobic stretch of 20 amino acids and a putative signal sequence cleavage site. Five putative N-glycosylation sites are also in the protein sequence. This data is consistent with the previous finding of carboxypeptidase yscS being a vacuolar peptidase. Chromosomal disruption of the CPS1 gene completely abolishes carboxypeptidase yscS activity. This protein is yet another member of the peptidases in S. cerevisiae involved in nitrogen metabolism.

Nitrogen sparing by 2-ketoisocaproate in parenterally fed rats

In rats receiving total parenteral nutrition with or without sodium 2-ketoisocaproate (KIC; 2.48 g.kg-1.day-1), L-[1-13C]leucine and [1-14C]KIC were constantly infused for 6 h. CO2 production, 14CO2 production, 13CO2 enrichment, urinary urea nitrogen (N) plus ammonia N and total urinary N were measured. Whole body protein synthesis (S) was calculated in non-KIC-infused rats and also in unfed rats infused with [1-14C]leucine from fractional oxidation of labeled leucine (1-F), where F is fractional utilization for protein synthesis, and urea N plus ammonia N excretion (C) as S = C x F/(1-F). Addition of KIC caused a significant reduction in N excretion and a significant improvement in N balance. Fractional oxidation of labeled KIC increased, whereas fractional utilization of labeled KIC for protein synthesis decreased, but the extent of incorporation of infused KIC into newly synthesized protein (as leucine) amounted to at least 40% of the total rate of leucine incorporation into newly synthesized whole body protein. We conclude that addition of KIC spares N in parenterally fed rats and becomes a major source of leucine for protein synthesis.