Comparative nutrition and metabolism: explication of open questions with emphasis on protein and amino acids

Dietary cystine restriction increases the proliferative capacity of the small intestine of mice

Currently, over 88 million people are estimated to have adopted a vegan or vegetarian diet. Cysteine is a semi-essential amino acid, which availability is largely dependent on dietary intake of meat, eggs and whole grains. Vegan/vegetarian diets are therefore inherently low in cysteine. Sufficient uptake of cysteine is crucial, as it serves as substrate for protein synthesis and can be converted to taurine and glutathione. We found earlier that intermolecular cystine bridges are essential for the barrier function of the intestinal mucus layer. Therefore, we now investigate the effect of low dietary cystine on the intestine. Mice (8/group) received a high fat diet with a normal or low cystine concentration for 2 weeks. We observed no changes in plasma methionine, cysteine, taurine or glutathione levels or bile acid conjugation after 2 weeks of low cystine feeding. In the colon, dietary cystine restriction results in an increase in goblet cell numbers, and a borderline significant increase mucus layer thickness. Gut microbiome composition and expression of stem cell markers did not change on the low cystine diet. Remarkably, stem cell markers, as well as the proliferation marker Ki67, were increased upon cystine restriction in the small intestine. In line with this, gene set enrichment analysis indicated enrichment of Wnt signaling in the small intestine of mice on the low cystine diet, indicative of increased epithelial proliferation. In conclusion, 2 weeks of cystine restriction did not result in apparent systemic effects, but the low cystine diet increased the proliferative capacity specifically of the small intestine and induced the number of goblet cells in the colon.

Dietary glycine equivalent and standardized ileal digestible methionine + cysteine levels for male broiler chickens fed low-crude-protein diets

This study was conducted to determine the optimum dietary glycine equivalent (Glyequi) level in low-crude-protein diets of 181 g·kg−1 containing varied concentrations of standardized ileal digestible (SID) methionine + cysteine (Met + Cys) for broiler chicks (1–21 d old). A total of 1275, 1-d-old Cobb-Vantress® male broilers were distributed in a 5 × 3 factorial arrangement with a completely randomized design of 15 treatments with five replicates of 17 birds each. Treatments consisted of five levels of dietary Glyequi (14.9, 16.4, 17.9, 19.4, and 20.6 g·kg−1) and three concentrations of SID Met + Cys (7.70, 9.0, and 10.3 g·kg−1). Interactions between Glyequi and SID Met + Cys levels were observed for feed:gain (P = 0.055) and breast meat yield (BMY) (P = 0.017). In 7.7 and 9.0 g SID Met + Cys·kg−1 diets, optimal feed:gain and increased BMY were observed at Glyequi levels not lower than 17.9 g·kg−1. In 10.3 g SID Met + Cys·kg−1 diet, a lower feed:gain was achieved at 19.4 g Glyequi·kg−1. Therefore, a minimum dietary level of 17.9 g Glyequi·kg−1 is needed to increase growth of broilers fed diets containing 7.7 or 9.0 g·kg−1 SID Met + Cys, whereas 19.4 g·kg−1 Glyequi is necessary in diets containing 10.3 g·kg−1 SID Met + Cys for optimum growth.

Centennial Review: A meta-analysis of the significance of Eimeria infection on apparent ileal amino acid digestibility in broiler chickens

Eimeria infections impair digestive tract capacity and barrier function leading to poor growth and feed efficiency. A meta-analysis approach was used to evaluate and quantify impact of Eimeria infection on the apparent ileal digestibility (AID) of amino acids (AA) in broiler chickens. A database composed of 6 articles with a total of 21 experiments was built for the effect of challenge type (a mix of Eimeria spp. vs. E. acervulina) and subdatabase of 3 articles with a total of 15 experiments for the effect of E. acervulina dose response. Regression models were fitted with the mixed model procedure in Minitab 19 with fixed effects of challenge, species, and their interactions. For the sub database, the mixed model procedure was used to fit regression models and identify a linear or quadratic response to dose. Challenge decreased AID (P < 0.05) of both dispensable and indispensable AA except for Trp. Specifically, the largest depression was observed for Cys, Thr, Tyr, Ala, and Val with the magnitude of difference of 8.7, 5.4, 5.2, 5.1, and 4.9%, respectively for challenged vs. unchallenged birds. The type of challenge affected (P < 0.05) AID of AA with exception of Cys, Tyr, Ala, Ser, Leu, Asp, Gly, and Pro. E. acervulina challenge had larger negative effects on AID of Ile, Leu, and Val. Moreover, E. acervulina linearly decreased (P < 0.05) AID of all indispensable and dispensable AA except for Trp and quadratically (P < 0.05) decreased AID of all AA except Cys, Met, Arg, and Trp. The largest linear decrease due to E. acervulina dose was seen for AID of Cys, followed by Ala, Val, Thr, and Ile. Although, AID of Trp was not affected by E. acervulina challenge, mixed Eimeria species challenge decreased (P < 0.05) AID of Trp. Overall, the results confirmed that an Eimeria infection negatively impacted AA digestibility/utilization. The ranking of the most affected AA suggested ground for nutritional intervention during subclinical field Eimeria infections or vaccination programs.

Potential Implications of Citrulline and Quercetin on Gut Functioning of Monogastric Animals and Humans: A Comprehensive Review

The importance of gut health in animal welfare and wellbeing is undisputable. The intestinal microbiota plays an essential role in the metabolic, nutritional, physiological, and immunological processes of animals. Therefore, the rapid development of dietary supplements to improve gut functions and homeostasis is imminent. Recent studies have uncovered the beneficial effects of dietary supplements on the immune response, microbiota, gut homeostasis, and intestinal health. The application of citrulline (a functional gut biomarker) and quercetin (a known potent flavonoid) to promote gut functions has gained considerable interest as both bioactive substances possess anti-inflammatory, anti-oxidative, and immunomodulatory properties. Research has demonstrated that both citrulline and quercetin can mediate gut activities by combating disruptions to the intestinal integrity and alterations to the gut microbiota. In addition, citrulline and quercetin play crucial roles in maintaining intestinal immune tolerance and gut health. However, the synergistic benefits which these dietary supplements (citrulline and quercetin) may afford to simultaneously promote gut functions remain to be explored. Therefore, this review summarizes the modulatory effects of citrulline and quercetin on the intestinal integrity and gut microbiota, and further expounds on their potential synergistic roles to attenuate intestinal inflammation and promote gut health.

Cyst(e)ine fortification in low crude protein diet improves growth performance of broilers by modulating serum metabolite profile

This study was aimed to explore the metabolomical mechanisms for the potentially ameliorative effect of cyst(e)ine (Cys) fortification on growth performance of broilers fed low crude protein (CP) diet. A total of 432 1-d-old broilers were randomly divided into 6 groups, each of which received one of the following diets: normal-CP diet (positive control, PC), low-CP diet (negative control, NC), NC diet fortified with 0.05%, 0.1%, 0.15% or 0.2% of Cys. Samples were collected on d 42. Results showed that increasing Cys fortification quadratically elevated (P < 0.05) the accumulative growth performance and leg muscle yield of broilers fed NC diet, with 0.1% being the optimal dose. Thus, samples from PC, NC and NC plus 0.1% Cys (NCC) groups were selected for further analysis. Both dietary CP reduction and fortification of 0.1% Cys in NC diet caused complex changes (P < 0.05) in serum amino acids and some other metabolites primarily involved in lipid metabolism. Multiple lipogenesis-related pathways were regulated (P < 0.05) following Cys fortification in NC diet, which could at least partially interpret the benefit of Cys fortification in NC diet on broiler performance. In conclusion, fortifying low-CP diet with 0.1% Cys promoted the growth performance of broilers probably through modulating serum metabolite profile.

Amino Acids in Dog Nutrition and Health

The dog has assumed a prominent role in human society. Associated with that status, diet choices for companion dogs have begun to reflect the personal preferences of the owners, with greater emphasis on specialty diets such as organic, vegan/vegetarian, and omission or inclusion of specific ingredients. Despite consumer preferences and many marketing strategies employed, the diets must ensure nutritional adequacy for the dog; if not, health becomes compromised, sometimes severely. The most frequent consideration of consumers and dog food manufacturers is protein source and concentration with a growing emphasis on amino acid composition and bioavailability. Amino acids in general play diverse and critical roles in the dog, with specific amino acids being essential. This review covers what is known regarding amino acids in dog nutrition.

Dietary L-citrulline supplementation modulates nitric oxide synthesis and anti-oxidant status of laying hens during summer season

Background

L-citrulline (L-Cit), a non-protein amino acid, has been implicated in several physiological functions including anti-inflammatory, anti-oxidative, and hypothermic roles, however, there is a paucity of information with regards to its potential in poultry production.

Methods

This study was designed to investigate the effects of dietary L-Cit supplementation on the production performance, nitric oxide production, and antioxidant status of laying hens during summer period. Hy-Line Brown laying hens (n = 288, 34 weeks old) were allotted to four treatment, 6 replicates of 12 chickens each. Dietary treatments of control (basal diets), 0.25%, 0.50% and 1.00% L-Cit supplementation were fed to chickens for eight (8) weeks. Production performance, free amino acid profiles, nitric oxide production, and antioxidant properties were measured. Blood samples were collected at the 4^th and 8^th weeks of the experiment.

Results

Air temperature monitoring indicated an average daily minimum and maximum temperatures of 25.02 °C and 31.01 °C respectively. Dietary supplementation with L-Cit did not influence (P > 0.05) the production performance, and rectal temperature of laying hens. Egg shape index was increased (P < 0.05) with increasing levels of L-Cit. Serum-free content of arginine, citrulline, ornithine, tryptophan, histidine, GABA, and cystathionine were elevated, but taurine declined with L-Cit diets. Plasma nitric oxide (NO_x) concentration was highest at 1% L-Cit. Likewise, nitric oxide synthase (NOS) activity for total NOS (tNOS) and inducible NOS (iNOS) were upregulated with increasing L-Cit levels, although, tNOS was not affected at the 4^th week. Anti-oxidant enzymes including catalase and superoxide dismutase (SOD) were increased with L-Cit supplementation, however, SOD activity was unchanged at 4^th week, while total anti-oxidant capacity increased at the 8^th week. L-Cit supplementation attenuated the extent of lipid peroxidation, and also inhibited glutathione peroxidase activity.

Conclusion

Dietary L-Cit supplementation modulated systemic arginine metabolism, nitric oxide synthesis, antioxidant defense system, and increased the egg shape index of laying hens during the summer season. 1% L-Cit supplementation proved most effective in potentiating these effects and may be adopted for feed formulation strategies.

Effect of dietary chelated copper and methionine and cysteine on performance, egg quality, and nutrient balance in brown laying hens from 20 to 49 wk old

Using 960 brown laying hens from 20 to 48 wk of age, in a 4 × 5 factorial arrangement, the effects on production, quality of eggs, and nutrient balance of analysed 18, 41, 61, and 111 mg kg−1of copper (Cu) and of 0.550%, 0.679%, 0.793%, 0.845%, and 0.948% of methionine and cysteine (Met + Cys) were evaluated. Treatments were administered to six replicate cages (eight hens per cage). At the 49th wk of age, 320 of these hens were kept under the same experimental conditions to evaluate the nutrient balance, and each treatment was allocated to four replicate cages (four hens per cage). The trend of interaction effect between Cu and Met + Cys levels was observed on egg weight and mass. The interaction between mineral and amino acid was characterized on egg quality variables. Quadratic equations indicated that increasing the dietary level of Cu reduced the estimate requirement of Met + Cys for hens. Across the entire experimental period, the total estimated Met + Cys level was 0.755% ± 0.021% based on the performance variables. As Cu increased in the diet, it decreased the estimated Met + Cys level to ensure egg weight, mass, and egg quality. Level of chelated Cu above 23 mg kg−1may negatively affect the egg quality.

Applications for α-lactalbumin in human nutrition

α-Lactalbumin is a whey protein that constitutes approximately 22% of the proteins in human milk and approximately 3.5% of those in bovine milk. Within the mammary gland, α-lactalbumin plays a central role in milk production as part of the lactose synthase complex required for lactose formation, which drives milk volume. It is an important source of bioactive peptides and essential amino acids, including tryptophan, lysine, branched-chain amino acids, and sulfur-containing amino acids, all of which are crucial for infant nutrition. α-Lactalbumin contributes to infant development, and the commercial availability of α-lactalbumin allows infant formulas to be reformulated to have a reduced protein content. Likewise, because of its physical characteristics, which include water solubility and heat stability, α-lactalbumin has the potential to be added to food products as a supplemental protein. It also has potential as a nutritional supplement to support neurological function and sleep in adults, owing to its unique tryptophan content. Other components of α-lactalbumin that may have usefulness in nutritional supplements include the branched-chain amino acid leucine, which promotes protein accretion in skeletal muscle, and bioactive peptides, which possess prebiotic and antibacterial properties. This review describes the characteristics of α-lactalbumin and examines the potential applications of α-lactalbumin for human health.

Characterization of aminoaciduria and hypoaminoacidemia in dogs with hepatocutaneous syndrome

OBJECTIVE To characterize aminoaciduria and plasma amino acid concentrations in dogs with hepatocutaneous syndrome (HCS). ANIMALS 20 client-owned dogs of various breeds and ages. PROCEDURES HCS was definitively diagnosed on the basis of liver biopsy specimens (n = 12), gross and histologic appearance of skin lesions (4), and examination of skin and liver biopsy specimens (2) and presumptively diagnosed on the basis of cutaneous lesions with compatible clinicopathologic and hepatic ultrasonographic (honeycomb or Swiss cheese pattern) findings (2). Amino acid concentrations in heparinized plasma and urine (samples obtained within 8 hours of each other) were measured by use of ion exchange chromatography. Urine creatinine concentration was used to normalize urine amino acid concentrations. Plasma amino acid values were compared relative to mean reference values; urine-corrected amino acid values were compared relative to maximal reference values. RESULTS All dogs had generalized hypoaminoacidemia, with numerous amino acid concentrations < 50% of mean reference values. The most consistent and severe abnormalities involved glutamine, proline, cysteine, and hydroxyproline, and all dogs had marked lysinuria. Urine amino acids exceeding maximum reference values (value > 1.0) included lysine, 1-methylhistidine, and proline. CONCLUSIONS AND CLINICAL RELEVANCE Hypoaminoacidemia in dogs with HCS prominently involved amino acids associated with the urea cycle and synthesis of glutathione and collagen. Marked lysinuria and prolinuria implicated dysfunction of specific amino acid transporters and wasting of amino acids essential for collagen synthesis. These findings may provide a means for tailoring nutritional support and for facilitating HCS diagnosis.

Nutritional regulation of the anabolic fate of amino acids within the liver in mammals: concepts arising from in vivo studies

At the crossroad between nutrient supply and requirements, the liver plays a central role in partitioning nitrogenous nutrients among tissues. The present review examines the utilisation of amino acids (AA) within the liver in various physiopathological states in mammals and how the fates of AA are regulated. AA uptake by the liver is generally driven by the net portal appearance of AA. This coordination is lost when demands by peripheral tissues is important (rapid growth or lactation), or when certain metabolic pathways within the liver become a priority (synthesis of acute-phase proteins). Data obtained in various species have shown that oxidation of AA and export protein synthesis usually responds to nutrient supply. Gluconeogenesis from AA is less dependent on hepatic delivery and the nature of nutrients supplied, and hormones like insulin are involved in the regulatory processes. Gluconeogenesis is regulated by nutritional factors very differently between mammals (glucose absorbed from the diet is important in single-stomached animals, while in carnivores, glucose from endogenous origin is key). The underlying mechanisms explaining how the liver adapts its AA utilisation to the body requirements are complex. The highly adaptable hepatic metabolism must be capable to deal with the various nutritional/physiological challenges that mammals have to face to maintain homeostasis. Whereas the liver responds generally to nutritional parameters in various physiological states occurring throughout life, other complex signalling pathways at systemic and tissue level (hormones, cytokines, nutrients, etc.) are involved additionally in specific physiological/nutritional states to prioritise certain metabolic pathways (pathological states or when nutritional requirements are uncovered).

Endogenous Synthesis of Amino Acids Limits Growth, Lactation, and Reproduction in Animals

Amino acids (AAs) are building blocks of protein. Eight AAs (Ala, Asn, Asp, Glu, Gln, Gly, Pro, and Ser) are formed by all animals, whereas de novo synthesis of Arg occurs in a species-specific manner in most mammals (e.g., humans, pigs, and rats). Synthesizable AAs were traditionally classified as nutritionally nonessential for animals, because they were thought to be formed in sufficient amounts. However, this assumption is not supported by evidence showing that 1) rats grow slowly when their diets do not contain Arg, Glu, or Gln despite adequate provision of all other proteinogenous AAs; 2) pigs cannot achieve maximum growth, lactation, or reproduction performance when fed corn- and soybean meal-based diets meeting National Research Council-recommended requirements of protein and AAs without supplemental Arg, Glu, Gln, Gly, or Pro; 3) chickens exhibit increases in lean tissue gain and feed efficiency when their diets are supplemented with Glu, Gln, Gly, and Pro; 4) lactating cows cannot obtain maximum milk protein production without a postruminal supply of Gln or Pro; 5) fish cannot achieve maximum growth when diets do not contain Gln or Pro; and 6) men fail to sustain spermatogenesis when fed an Arg-deficient diet. Quantitative analysis of nitrogen metabolism showed that AA synthesis in animals is constrained by both precursor availability and enzyme activity. Taken together, these findings support the conclusion that the endogenous synthesis of AAs limits growth, lactation, and reproduction in animals. This new knowledge can guide the optimization of human nutrition for improving health and well-being.

Biochemical and physiological bases for utilization of dietary amino acids by young Pigs

Protein is quantitatively the most expensive nutrient in swine diets. Hence it is imperative to understand the physiological roles played by amino acids in growth, development, lactation, reproduction, and health of pigs to improve their protein nutrition and reduce the costs of pork production. Due to incomplete knowledge of amino acid biochemistry and nutrition, it was traditionally assumed that neonatal, post-weaning, growing-finishing, and gestating pigs could synthesize sufficient amounts of all "nutritionally nonessential amino acids" (NEAA) to support maximum production performance. Therefore, over the past 50 years, much emphasis has been placed on dietary requirements of nutritionally essential amino acids as building blocks for tissue proteins. However, a large body of literature shows that NEAA, particularly glutamine, glutamate, arginine and proline regulate physiological functions via cell signaling pathways, such as mammalian target of rapamycin, AMP-activated protein kinase, extracellular signal-related kinase, Jun kinase, mitogen-activated protein kinase, and NEAA-derived gaseous molecules (e.g., nitric oxide, carbon monoxide, and hydrogen sulfide). Available evidence shows that under current feeding programs, only 70% and 55% of dietary amino acids are deposited as tissue proteins in 14-day-old sow-reared piglets and in 30-day-old pigs weaned at 21 days of age, respectively. Therefore, there is an urgent need to understand the roles and dietary requirements of NEAA in swine nutrition. This review highlights the basic biochemistry and physiology of absorption and utilization of amino acids in young pigs to enhance the efficacy of utilization of dietary protein and to minimize excretion of nitrogenous wastes from the body.

Dietary l-leucine supplementation of lactating rats results in a tendency to increase lean/fat ratio associated to lower orexigenic neuropeptide expression in hypothalamus

The aim of this study was to assess the effects of dietary leucine supplementation in lactating dams, particularly on energy homeostasis through signaling mechanisms in the central nervous system. Dams were fed ad libitum with standard diet during pregnancy (control dams) or supplemented with 2% leucine (leucine-supplemented dams) from delivery onwards. Food intake, body weight and composition were periodically recorded. Hypothalamus was collected at the end of lactation, and the expression of neuropeptide Y (NPY), agouti-related protein (AgRP) pro-opiomelanocortin (POMC), cocaine and amphetamine regulated transcript (CART), insulin receptor (InsR), ghrelin receptor (GSHR), melanocortin receptor (MCR4), leptin receptor (Ob-Rb) and suppressor of cytokine signaling 3 (SOCS3) were analyzed. Dietary leucine supplementation to lactating rats increased plasma leucine by 56%, modulated body composition and contributed to a tendency of higher ratio of lean/fat mass content of dams during lactation, without affecting food intake, thermogenesis capacity or body or tissue/organs weights. No differences in body weight of offspring from control and leucine-supplemented dams were found. The expression of orexigenic peptides (NPY and AgRP) decreased in leucine-dams, whereas the expression of anorexigenic peptides (POMC and CART), the hypothalamic receptors of insulin, ghrelin, melanocortin and leptin and SOCS3 did not change by leucine supplementation. In conclusion, increased leucine intake during lactation may contribute to a healthier profile of body composition in dams, without compromising the growth and development of the progeny by a mechanism associated with lower expression of orexigenic neuropeptides in hypothalamus.

The interactive effects of glycine, total sulfur amino acids, and lysine supplementation to corn-soybean meal diets on growth performance and serum uric acid and urea concentrations in broilers

Four experiments were conducted to determine the interactive effects of Gly, TSAA, and Lys in corn-soybean meal diets on growth performance of broilers. All experiments were conducted with female Ross x Ross 308 or 708 broilers in brooder batteries from 0 to 18 d posthatching. Treatments had 5 to 8 replications with 5 or 6 broilers per replicate pen. Diets in all experiments were fed without or with Gly (2.32% total Gly + Ser). All diets contained 0.25% l-Lys.HCl except in experiment 1, where no crystalline Lys was added. In experiment 1, the total dietary Lys level was 1.26% with TSAA:Lys of 0.72 and 0.76. Increasing TSAA:Lys increased (P < 0.07) G:F. The main effect of Gly was not significant for ADG, ADFI, or G:F; however, G:F was increased by Gly in broilers fed 0.72 but not in those fed 0.76 TSAA:Lys (Gly x TSAA:Lys, P < 0.03). In experiment 2, the total dietary Lys level was 1.26% with TSAA:Lys of 0.51, 0.68, 0.72, and 0.76. Glycine addition did not affect ADG, ADFI, or G:F; however, increasing TSAA:Lys linearly increased (P < 0.01) ADG, ADFI, and G:F and the response was quadratic for ADG and G:F. Experiment 3 was similar to experiment 2 except the total dietary Lys level was 1.35%. Glycine addition increased (P < 0.03) G:F and decreased (P < 0.04) serum uric acid (SUA) and serum urea N concentrations. Also, increasing TSAA:Lys linearly and quadratically (P < 0.02) increased ADG, ADFI, and G:F. In experiment 4, broilers were fed 2 levels of total dietary Lys (1.26 and 1.35%), 3 levels of TSAA:Lys (0.72, 0.76, and 0.80), and without or with Gly supplementation up to a total of 2.32% Gly + Ser. Glycine addition increased ADG (P < 0.02) and G:F (P < 0.01). The increase in G:F with Gly was not the same for all TSAA:Lys (Gly x TSAA:Lys, P < 0.07). Increasing Lys increased (P < 0.01 to 0.10) ADG, ADFI, and G:F. Glycine addition increased ADG and ADFI more in broilers fed 1.35% Lys than in those fed 1.26% Lys (Lys x Gly, P < 0.09). Glycine addition increased SUA in broilers fed 1.26% Lys but decreased SUA in broilers fed 1.35% Lys (P < 0.01). Glycine addition decreased SUA in broilers fed the TSAA:Lys of 0.80 but not at the other TSAA:Lys (P < 0.08). These data indicate that Gly increased G:F and decreased SUA in diets with 1.35% Lys and excess TSAA.

Mammals reduce methionine-S-sulfoxide with MsrA and are unable to reduce methionine-R-sulfoxide, and this function can be restored with a yeast reductase

Methionine is an essential amino acid in mammals at the junction of methylation, protein synthesis, and sulfur pathways. However, this amino acid is highly susceptible to oxidation, resulting in a mixture of methionine-S-sulfoxide and methionine-R-sulfoxide. Whether methionine is quantitatively regenerated from these compounds is unknown. Here we report that SK-Hep1 hepatocytes grew on methionine-S-sulfoxide and consumed this compound by import and methionine-S-sulfoxide reductase (MsrA)-dependent reduction, but methionine-R-sulfoxide reductases were not involved in this process, and methionine-R-sulfoxide could not be used by the cells. However, SK-Hep1 cells expressing a yeast free methionine-R-sulfoxide reductase proliferated in the presence of either sulfoxide, reduced them, and showed increased resistance to oxidative stress. Only methionine-R-sulfoxide was detected in the plasma of wild type mice, but both sulfoxides were in the plasma of MsrA knock-out mice. These results show that mammals can support methionine metabolism by reduction of methionine-S-sulfoxide, that this process is dependent on MsrA, that mammals are inherently deficient in the reduction of methionine-R-sulfoxide, and that expression of yeast free methionine-R-sulfoxide reductase can fully compensate for this deficiency.

Carbonic anhydrase activators: kinetic and X-ray crystallographic study for the interaction of D- and L-tryptophan with the mammalian isoforms I-XIV

An activation study of mammalian carbonic anhydrase (CA, EC 4.2.1.1) isoforms I-XIV with D- and L-tryptophan has been performed both by means of kinetic and X-ray crystallographic techniques. These compounds show a time dependent activity against isozyme CA II, with activation constants of 1.13 microM for L-Trp and 0.37 microM for D-Trp, respectively, after 24 h of incubation between enzyme and activator. The high resolution X-ray crystal structure of the hCA II-D-Trp adduct revealed the activator to bind in a totally unprecedented way to the enzyme active site as compared to histamine, L-/D-Phe, L-/D-His or L-adrenaline. D-Trp is anchored at the edge of the CA II active site entrance, strongly interacting with amino acid residues Asp130, Phe131 and Gly132 as well as with a loop of a second symmetry related protein molecule from the asymmetric unit, by means of hydrogen bonds and several weak van der Waals interactions involving Glu234, Gly235, Glu236 and Glu238. Thus, a second activator binding site (B) within the CA II cavity has been detected, where only D-Trp was shown so far to bind, in addition to the activator binding site A, in which histamine, L-/D-Phe, and L-/D-His are bound. These findings explain the strong affinity of D-Trp for CA II and may be useful for designing novel classes of CA activators by using this compound as lead molecule.

Individual response of growing pigs to sulphur amino acid intake

Two N balance experiments were conducted to study the individual response of growing pigs to limiting amino acid (AA) intake. Series of fifteen diets with increasing concentration of sulphur amino acids (SAA, Expt 1) or methionine in the presence of excess cystine (Expt 2) were fed sequentially to nine pigs during a 15-day experimental period. The concentration of the AA under test ranged from 50% to 140% of the requirement while other essential AA were given in a 25% excess relative to the limiting AA. N retention was related to the limiting AA intake using rectilinear and curvilinear models. In Expt 1, the quadratic-plateau model fitted the individual data significantly better (p = 0.01) than the linear-plateau model. No difference was found between the two models in Expt. 2, presumably due to the sparing effect of excess cystine on methionine utilization. Exponential, saturation kinetics or four-parameter logistic models fitted to data for all pigs showed that their goodness of fit was similar to those of quadratic-plateau or linear-plateau models. Significant differences (p < 0.05) were found between individual plateau values for N retention within each experiment while the slopes of the regression lines did not significantly differ either in Expt 1 (p = 0.07) or Expt 2 (p = 0.45). There was a positive correlation between the slope and plateau values of the linear-plateau model in Expt 1 (r = 0.74, p = 0.02) but no significant correlation was found in Expt 2 (r = -0.48, p = 0.13). Marginal efficiencies of SAA and methionine utilization derived from the linear-plateau model were 0.43 and 0.65 respectively. Based on linear-plateau and quadratic-plateau models, daily requirements of SAA and methionine for a 50 kg pig were estimated to be 13.0 and 5.9 g and 14.3 and 6.1 g respectively.

Contribution of research with farm animals to protein metabolism concepts: a historical perspective

The roles of proteins, carbohydrates, fats, and micronutrients in animal and human nutrition were broadly described during the late 18th and 19th centuries, and knowledge in protein nutrition evolved from work with all species. Although much of the fundamental and theoretical research in protein metabolism during the 20th century was conducted with laboratory animals, basic protein nutrition research in farm animals complemented those efforts and led to the development and use of new investigative methods (particularly in amino acid nutrition) as well as use of animal models in furthering the understanding of human protein metabolism. All these efforts have led to a contemporary hybrid model of protein nutrition and metabolism applicable to both humans and animal species. Now in the 21st century, farm animals are used in fetal and pediatric nutrition research, and data accruing for excess amino acid feeding in research with farm animals provide direction for assessment of pharmacological effects of amino acids when consumed in excessive quantities. Thus, as nutritional science is moving forward into nutrigenomics, nutriproteomics, and metabolomics, farm animal and human nutrition research interactions will likely continue with genetically modified farm animals produced for agricultural reasons (improved function and product quality) or those produced with human genes introduced to generate even better models of human protein metabolism.