Plasma Free Amino Acid Concentrations Research Articles

Metabolic and hormonal factors as predictors of nitrogen retention in obese men consuming very low calorie diets

The ability to conserve body protein during very low calorie diets in ten obese men was observed to correlate with plasma free amino acid concentrations, urinary N τ-methylhistidine:creatinine ratios, resting oxygen consumption, and serum triiodothyronine levels. A diet consisting of only protein, 1.3 g/kg ideal body weight/24 h, was given for 40 days. Cumulative nitrogen deficit ranged from −64 g to −227 g. Nitrogen balance on days 36 to 40 ranged from +1.37 g 24 h to −3.30 g 24 h . Nitrogen balance during this period had a significant direct correlation with prediet concentrations of branched-chain amino acids ( r = 0.69 to 0.89), methionine ( r = 0.85), histidine ( r = 0.66), alanine ( r = 0.73), arginine ( r = 0.70), ornithine ( r = 0.66), total essential ( r = 0.87), and nonessential ( r = 0.68) amino acids, with initial serum levels of triiodothyronine ( r = 0.66) and with the fall in triiodothyronine over the 40 days ( r = 0.79). Initial resting oxygen consumption was directly correlated ( r = 0.78) with final nitrogen balance and inversely with total nitrogen loss ( r = −0.81). On day 0, triiodothyronine levels also correlated positively ( r ranging from 0.71 to 0.93) with plasma concentrations of several essential and nonessential amino acids. These correlations suggest that individuals who ultimately will or will not achieve nitrogen equilibrium during very low calorie diets can be identified prior to dieting. These data are consistent with the hypothesis that individuals with higher initial protein flux and triiodothyronine levels are better able to adjust the balance between synthesis and degradation to attain nitrogen equilibrium during hypocaloric dieting.

Effect of Aspartame Loading on Plasma and Erythrocyte Free Amino Acid Concentrations in One-Year-Old Infants

Aspartame is a new dipeptide sweetener. It has been suggested that infants metabolize its constituent amino acids (aspartate and phenylalanine) less well than adults. To test this hypothesis, 24 1-year-old infants were administered 34, 50 and 100 mg/kg body weight aspartame in cherry-flavored beverage mix. Plasma amino acid concentrations and the areas under the plasma concentration-time curves (AUC) were determined and were compared with values in adults administered equivalent doses. The doses studied include the 99th percentile of projected ingestion for adults (34 mg/kg), a very high use dose (50 mg/kg body weight), and a potentially abusive dose (100 mg/kg body weight). Plasma aspartate concentrations did not change > 0.05) at aspartame doses of 34 and 50 mg/kg body weight, but did increase significantly at the 100 mg/kg body weight dose. The change over base line was similar in infants and adults. Aspartame dosing significantly increased both the mean peak plasma phenylalanine concentration and the plasma phenylalanine AUC value in proportion to dose. Mean (±SD) peak plasma phenylalanine concentrations in infants were 9.87 ± 1.44, 11.6 ± 4.44 and 22.3 ±11.5 µmol/100 ml at aspartame doses of 34, 50 and 100 mg/kg body weight, respectively. Values in infants were similar to those noted in adults. The data do not support the suggestion that infants metabolize the amino acids of aspartame less well than adults.

The digestion of barley-based diets by cattle: the effect of feeding of three diets containing different amounts of formaldehyde-treated soybean meal

Six growing cattle, with intestinal fistulae, were fed on barley-based diets to which were added increments of formaldehyde-treated soybean meal; the latter was substituted for whole-grain barley. The digestion of organic matter (OM), �-linked glucose polymer (starch), nitrogen (N) and rumen volatile fatty acids (VFA) were measured at a restricted level of intake. The cattle were offered air-dried feed at 3.4 kg per head daily, or approximately ad libitum (i.e. 4.2 kg air-dried feed per head per day). The three diets contained 19.7, 27.8 or 42.9 g nitrogen (N) per kg and were fed in a Latin-square design. When the feed was offered ad libitum there was a significant increase in OM digestibility, from 78% on the lowest N diet to 84% on the highest N diet. Relatively large quantities of starch (140-477 g/day) entered and were apparently digested in the small intestine, especially on the 19.7 g N/kg dry matter (the highest starch diet) on ad libitum feeding. The molar proportions of VFA in rumen liquor largely reflected the amount of starch which was fermented in the rumen. The digestion of nitrogen was characterized by a net gain in flow to the duodenum compared with intake. There was a significant increase in the amount of N apparently digested in the small intestines on the 42.9 g N/kg dry matter diet. The proportion of microbial N at the duodenum declined as more formaldehyde-treated soybean meal was added to the diet. Compared with that of the lowest N diet, the amount of amino acids entering and being apparently digested in the small intestines doubled in the highest N diet, and the concentrations of plasma-free amino acids reflected this. The feed intake comparison indicated that differences in interpretations of digestion studies were likely if animals were fed solely at restricted intakes. The main discrepancies were in OM digestibility, starch digestion in the small intestine, the proportion of microbial N flow at the duodenum and in the estimation of amino acid absorption and requirement.

Effect of diet and infusion of volatile fatty acids into the rumen on the concentration of plasma free amino acids in sheep

The effect of supplementing barley diets with urea (U), extracted decorticated groundnut meal (GNM) or Peruvian fish meal (PFM) on plasma free amino acid concentrations in sheep have been examined and the first limiting amino acid has been indicated by measuring the changes in the concentration of the plasma essential amino acids (PEAA) during a rumen infusions of a volatile fatty acid (VFA) mixture. 2. Three wethers fitted rumen and re-entrant duodenal cannulas were given isonitrogenous, isoenergetic diets containing (g/kg dry matter (DM) U 20, GNM 106 and PFM 78, the crude protein (nitrogen x 6.25) contents being 139, 145 and 148 respectively. The sheep were fed hourly, the mean daily DM intake being 0.634 kg. 3. Plasma concentrations of valine, threonine, lysine, isoleucine and leucine were linearly related to their concentrations in duodenal digesta. 4. A VFA mixture was infused into the rumen for 6 h to supply (mmol/min) acetate 1.47, propionate 0.22 and n-butyrate 0.27. Blood samples were taken 6 h before, during and 12 h after the end of the infusion. 5. The concentration of all PEAA decreased relative to the pre-infusion and post-infusion controls but there were no significant differences between diets. 6. The mean decrease in concentration averaged over all three diets showed that the decrease in concentration of methionine (41.5%) was far greater than for any other essential amino acid suggesting that under these conditions methionine was the first limiting amino acid.

Plasma amino acid changes in Tilapia nilotica fed a casein and a corresponding free amino acid diet.

Satarved Tilapia nilotica were fed a casein diet and an amino acid diet of similar composition. The change in concentrations of plasma-free amino acids of Tilapia at 0, 2, 4, 8, 12 and 24 hours after adminstering the two diets was examined, With respect to the casein diet, all plasma-free essential amino acids attained their maximal values at 4 hours after feeding, and then declied to the fasting levels within 24 hours. with the amino acid diet, all plasma-free essential amino acids peaked at 2 hours, and returned to their fasting levels within 4 to 8 hours. Free non-essential amino acids showed unique patterns of change in the plasma of Tilapia after both the casein diet and the free amino acid diet were administered.

Plasma and cerebrospinal fluid free amino acid concentration in post-traumatic cerebral oedema in patients with shock

The concentrations of free amino acids in plasma and cerebrospinal fluid (CSF) in 15 patients with post-traumatic cerebral oedema with hyperventilatory syndrome have been analyzed. Hypotheses are proffered to interpret the observed alterations of amino acids cerebral metabolism in this condition.

Effects of a glandless cottonseed protein diet on fasting plasma amino acid levels in college women

Plasma amino acids were determined and correlated to the level of dietary amino acids consumed over a 42-day period. Six college women, ages 19 to 23, were fed meals in which 99% of the dietary protein was supplied by glandless cottonseed flour. The protein content was decreased weekly from 14.6 to 9.9, 8.7, 7.5, 6.9, and 6.3 g nitrogen per day, until that amount was found that would not maintain nitrogen equilibrium. Fasting blood samples were obtained after subjects had consumed a specific protein level for 1 week. Significant (P less than 0.05) decreases in fasting plasma free amino acid levels occurred from day 0 to 7 of the study for threonine, proline, isoleucine, leucine, tyrosine, and lysine. There were no significant differences in these plasma amino acids thereafter. Of the essential amino acids, leucine, valine, histidine, and lysine appeared to have similar graphical trends between the plasma and dietary amino acid concentrations over the entire 6-week period. However, only leucine had a significant (P less than 0.05) correlation. Results indicated that fasting plasma free amino acid concentrations of young women on a cottonseed protein diet appear to drop initially, but rarely fall beyond the realms of normal values during nitrogen equilibrium.

Lysine Requirement of Broilers as Influenced by Environmental Temperatures

Two experiments were conducted to determine the influence of 15.6 and 29.4°C. environmental temperatures on 2- to 4-week broiler lysine requirements. Weights for 4-week-old cockerels were maximum when either 1.10% dietary lysine in the 15.6°C. environment or 1.00% dietary lysine in the 29.4° C. environment were fed. Feed was used more efficiently by 4-week old cockerels fed either 1.10% dietary lysine in the 15.6°C. environment or 0.95% dietary lysine in the 29.4° C. environment.Plasma free lysine concentrations from 4-week-old cockerels increased as dietary lysine increased. Total plasma free amino acid concentrations from chicks grown in a 15.6°C. environment were approximately 25% greater than from chicks grown at 29.4° C. Total plasma free amino acids for 4-week-old cockerels peaked when 1.05% dietary lysine in the cool environment and 0.95% dietary lysine in the warm environment were fed.

Effects of dietary histidine and arginine on plasma amino acid and urea concentrations of men fed a low nitrogen diet

The effects of dietary histidine and arginine on fasting and 1 and 2 hour postprandial plasma free amino acid and urea concentrations were studied in six young men. For 1 week each, they were fed six different diets containing 6.3 g of nitrogen daily. Each diet contained eight indispensable amino acids, cystine and tyrosine proportioned as in casein and a different mixture of dispensable nitrogen: A) six dispensable amino acids plus argine (diet 1) or plus histidine and arginine (diet 2) in the casein pattern, or B) an isonitrogenous amount of glycine and diammonium citrate alone (diet 3), with histidine (diet 4), with arginine (diet 5) or with histidine and arginine (diet 6). The fasting plasma concentrations of the seven indispensable amino acids assayed and their similar postprandial patterns were unaffected by the dietary treatments. Both fasting and postprandial plasma histidine concentrations were significantly lower when the histidine-low diets were fed than when the histidine-supplemented diets were fed. Histidine supplementation promoted a reduction in fasting plasma urea nitrogens. Proline concentrations were lowered significantly when proline was removed from the dietary amino acid mixtures, but plasma arginine concentrations were unaffected by arginine removal. Plasma histidine was maintained at lower concentrations in dietary histidine deficiency than when histidine was added to the low nitrogen diets.

Plasma an intraerythrocyte amino-acid levels during and after haemodialysis in acute renal failure

A study is carried out on the variations of plasma and blood red cells free amino acid concentrations secondary to haemodialysis in patients suffering from acute renal failure. A reduction in plasma free amino acid pool has been observed in patients undergoing to many periodic haemosialysis, but no significant differences occur in plasma aminogram between before and after a single dyalitic procedure. Significant alterations were also observed in blood red cells aminogram, and this may be interpreted as reflex of intracellular omeostatic mechanisms for the maintenance of normal plasma free aminoacid pattern.

Relation between Liver Amino Acid-Catabolizing Enzymes and Free Amino Acids of Liver and Plasma in Adult Cockerels Fed Diets Containing Graded Levels of Protein

Activities of liver amino acid-catabolizing enzymes and liver and plasma free amino acid concentrations in adult cockerels fed diets containing 3% to 21% casein were determined 2 hours after a meal. Liver tryptophan pyrrolase activity and liver tryptophan increased with an increase in dietary casein level, but plasma tryptophan decreased with the increase dietary casein level. As the dietary casein level increased, liver lysine-ketoglutarate reductase activity decreased, but liver and plasma lysine increased proportionally, and the rate of increase was larger in the plasma than in the liver. Liver phenylalanine hydroxylase activity increased with the increase in dietary casein level from 3% to 12%, and thereafter remained unchanged. Reflecting the change of this enzyme, phenylalanine increased in the liver and decreased in the plasma with the increase in dietary casein level from 3% to 12%, and thereafter the rate of increase in liver phenylalanine became small and plasms phenylalanine increased. Liver tyrosine was not influenced by the dietary casein level, whereas plasma tyrosine increased sharply from 3% to 12%, and thereafter the rate of increase decreased. Thus, the difference between liver and plasma free amino acid responses might be due to the changes in the activities of liver amino acid-catabolizing enzymes.

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, phenylalanine, 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.

Amino acid metabolism in the piglet: 2. Influence of fasting on plasma free amino acid concentration and in vivo oxidation of methionine, isoleucine and threonine

1. The influence of a 24 h fast on the concentrations of free amino acids in the plasma, and upon the oxidation rates of methionine, isoleucine and threonine was studied (using early weaned, 4-week-old piglets which were receiving a semi-purified diet.2. There was no change in the total concentration of the essential amino acids as a result of the 24 h fast: the concentration of the branched-chain amino acids increased, but the effect of this was offset by decreases in the concentrations of arginine, histidine, lysine, methionine and phenylalanine. There was a reduction in the concentration of the non-essential amino acids.3. The piglets received infusions of L-[1-14C]methionine, L-[U-14C]isoleucine and L-[U-14C]threonine, and the recovery of the label in carbon dioxide was determined. Less than 5% of the activity from methionine was recovered in the CO2 from the fed piglets, whereas 12% was recovered from the fasted piglets. The corresponding values with threonine were 11 and 19% but there was no effect of fasting on the recovery of the label from isoleucine in CO2.4. The initial dilution of a single dose of a labelled amino acid infused into the bloodstream depends on the plasma concentration of the amino acid. Nutritional regimens may effect the free amino acid concentration in the plasma. Thus comparisons based upon direct determination of activity recovered in CO2 from the labelled dose of an amino acid with animals on different nutritional regimens could be misleading, unless the differences in the concentrations of the amino acid in the plasma are considered.

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.

Variation de la concentration des acides amines libres du plasma au cours du cycle reproducteur chez le manchot empereur, aptenodytes forsteri

1. 1. Nine amino acids, alanine, serine, arginine, threonine, lysine, valine, glutamic acid, α-amino butyric acid and leucine, together represent 75–85 per cent of the total plasma amino acids in the emperor penguin; alanine itself represents one-third (100 μM/100 ml). 2. 2. A 40 per cent increase of total amino acids, especially branched (val, leu, ile), basic (lys, his, methyl-3-his) amino acids and methionine, was observed in males at the end of incubation (90–120 days fasting) or in animals undergoing severe starvation experimentally, except in those at the end of moulting. This could be attributed to high muscle proteolysis after lipid storage consumption. 3. 3. During egg formation an increase of plasma amino acids, mainly serine, was seen in females (330–440 μM/100 ml). 4. 4. At the beginning of moulting, during synthesis of the new feathers, plasma-free amino acid concentration increased from 310 to 510 μM/100 ml. The levels of basic (arg, lys, his), branched (leu, ile) amino acids, methionine, serine and glycine were particularly high. 5. 5. The total amino acids of fasting baby penguins, 4–6 months old, is normally similar to that of adults but is clearly higher in the postabsorptive state. 6. 6. Variations in total plasma amino acids of the emperor penguin seem to be correlated with the level and nature of metabolism, that is with breeding and moulting, rather than with fasting itself.

Nutritional evaluation of wheat 3. Effects of supplementation with lysine, threonine and methionine of diets based on wheat containing 13% crude protein on the performance of pigs

Summary1. Large White x Landrace pigs were used to study the effects of supplementation with limiting amino acids of diets based on wheat containing 13% crude protein. Measurements were made of growth rate, feed conversion, carcass composition, plasma-free amino acid concentrations, digestibility of dry matter, nitrogen and gross energy, nitrogen retention and metabolizable energy.2. A wheat diet supplemented with lysine and threonine, the firstand the second-limiting amino acids respectively, produced almost the same growth rate and feed conversion ratio as one supplemented with fish meal and meat meal. Methionine was probably the thirdlimiting amino acid, and additional supplementation with methionine produced a further small improvement in growth rate and feed conversion ratio to the point where they were equal to those on the diet supplemented with fish meal and meat meal.3. Supplementation of the wheat diet with lysine only produced the same growth rate and feed conversion ratio as a least-cost commercial diet; performance was, however, inferior to that on a wheat diet supplemented with fish meal and meat meal. The commercial diet had a lower dry-matter digestibility.4. Eye-muscle area of pigs on the wheat diet supplemented with lysine was similar to that of pigs on a wheat diet supplemented with fish meal and meat meal; however, backfat thickness was significantly lower on the latter diet.5. Except for threonine, plasma-free amino acid concentrations reflected with reasonable accuracy amino acid deficiencies in the diets.

Nutritional evaluation of wheat 4. Effects of supplementation with amino acids and protein of diets based on wheats containing 10% and 17% crude protein on the performance of growing pigs

Summary1. The effects of supplementing diets containing 10% or 17% crude protein wheat, vitamins and minerals with the limiting amino acids were studied with growing Large White x Landrace pigs. Performance was measured in terms of growth rate, feed conversion, carcass measurements, plasma-free amino acid concentrations, digestibility of dry matter, nitrogen and gross energy, nitrogen retention and metabolizable energy.2. With diets based on wheat containing 17% crude protein, a lysine supplement gave a slightly higher growth rate and a slightly lower feed conversion ratio than when fish meal and meat meal was the supplement.3. With diets based on wheat containing 10% crude protein, performance was significantly poorer when the diet was supplemented with the four most limiting amino acids (lysine, threonine, valine, methionine) than with fish meal and meat meal. Meat meal and soya bean meal appeared to be a good source of the limiting amino acids, other than lysine, when added to a diet based on wheat containing 10% crude protein.4. Eye-muscle area was lower and backfat thickness greater when diets based on wheat containing 10% crude protein were unsupplemented or supplemented with lysine than when they were supplemented with protein or with the four most limiting amino acids. However, no significant differences in backfat thickness were obtained between similar comparisons when the wheat contained 17% crude protein.

Effect of dietary protein level on plasma and tissue free amino acid concentrations in nursing lambs.

Nursing lambs bottle fed a 12% protein milk replacer lost weight, consumed less (P < .005) feed and had markedly lower plasma and tissue (muscle and liver) amino acid concentrations than the lambs receiving the 24 or 35% protein milk replacers. Feed intakes and weight gains were similar for lambs fed 24 or 35% protein milk replacers. As dietary protein intake increased, the concentration of essential amino acids rose in plasma and tissue pools, while nonessential amino acids stayed constant. The lambs fed the 12 and 35% protein milk replacer had higher (P < .01) plasma urea than the 24% protein group. In all lambs, plasma amino acid levels were higher 2 hr after than before feeding. Dietary protein intake did not affect plasma glucose levels.

Nutritional evaluation of wheat. 2. The sequence of limiting amino acids in wheats of different protein content as determined with growing rats

SUMMARY1. Weanling male rats were used in three experiments to evaluate the sequence of limiting amino acids for maximum growth with diets based on wheats containing 10, 13 or 17% crude protein (N×5·71).2. Lysine was the first-limiting, threonine the second-limiting, and valine or methionine the third- or fourth-limiting amino acid for growth rate and feed-conversion ratio of rats offered the diet based on wheat containing 10% crude protein. A further four amino acids (isoleucine, histidine, tryptophan and tyrosine) were limiting for feed-conversion ratio only.3. For the diet based on wheat containing 13% crude protein the sequence of limiting amino acids was lysine, threonine and methionine.4. Only lysine was limiting in the diet based on wheat containing 17% crude protein.5. Plasma-free amino-acid concentrations were found to be a valuable criterion for prediction of the first-limiting amino acid in diets.6. Improvement of growth and feed-conversion ratio was observed with diets based on wheat containing 17 or 13% crude protein when the limiting amino acids were supplemented to provide the recommended allowance. Further improvement in feed-conversion ratio was obtained when lysine and threonine were provided in excess of the recommended allowances.7. There was a lysine-threonine interaction affecting growth rate and feed-conversion ratio, and a lysine-me.thionine interaction affecting feed-conversion ratio.