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Dietary L-Homoserine Spares Threonine in Chicks1,2

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Dietary L-Homoserine Spares Threonine in Chicks1,2 The Journal of Nutrition Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions Dietary L-Homoserine Spares Threonine in Chicks1,2 Kasey I. Bryant, Ryan N. Dilger, Carl M. Parsons, and David H. Baker1,2* Department of Animal Sciences and Division of Nutritional Sciences, University of Illinois, Urbana, IL 61802 Abstract Downloaded from https://academic.oup.com/jn/article/139/7/1298/4670474 by guest on 30 September 2021 Four chick bioassays were conducted to evaluate the threonine (Thr) replacement value of L-homoserine (HS). Growth rate was increased (P , 0.05) by dietary addition of 800 mg L-HS/kg diet to a purified diet severely deficient in Thr or by the addition of 800 or 1000 mg of L-HS/kg diet to a corn-peanut meal diet distinctly deficient in Thr. The addition of an isomolar level of a-ketobutyrate, a catabolic product of both Thr and HS, did not elicit a response. Standard-curve methodology predicted a Thr replacement value of 38 6 9% for HS. Interactions (P , 0.01) were observed in assays 2 and 4 between dietary Thr adequacy and 800 or 1000 mg L-HS/kg supplementation. Thus, HS improved growth performance when added to a Thr-deficient diet (0.46 g Thr/100 g diet), but it decreased growth performance when added to the same diet containing surfeit Thr (0.80 g Thr/100 g diet). The results indicate that low levels of HS elicit a growth response in young chicks fed Thr-deficient diets. J. Nutr. 139: 1298–1302, 2009. Introduction individual chicks and pen food intakes were measured at the beginning 3 Homoserine (HS) occurs free (unbound to protein) in a number and end of each chick assay. Body weight gain, food intake, and food of plants and it is particularly rich in pea seedlings (1). It is also efficiency (gain:food ratio) were calculated for each replicate pen of formed during catabolism of the carbon skeleton of methionine chicks. (Met) in higher organisms (1). It is well established (2–8) that Individual proteinaceous ingredients as well as basal diets were plants, bacteria, and yeast can synthesize not only threonine analyzed for crude protein (CP), Thr, Met, cyst(e)ine, and HS as (Thr) but also Met from HS. Watanabe and Shimura (2,3) previously described (11). The L-HS used herein was synthesized by showed that at least 2 separate enzyme fractions are needed in Evonik Degussa (Hanau-Wolfgang, Germany). Our amino acid (AA) analysis indicated the product was .99% pure HS and contained no yeast and Neurospora for synthesis of Thr from HS. The first detectable Thr. involves HS kinase, which catalyzes the phosphorylation of HS via ATP. The second key enzyme in Thr biosynthesis from HS is Assay 1. The objective of this assay was to determine whether L-HS Thr synthetase and this enzyme requires pyridoxal phosphate. could spare the need for Thr in young chicks. The purified basal diet, Evidence for these conversions in higher organisms, however, singly deficient in Thr, was supplemented with either 800 mg Thr/kg diet does not exist. We present evidence here that HS has Thr or isomolar (800 mg/kg) or twice isomolar (1600 mg/kg) concentrations replacement bioactivity in young chicks. of L-HS at the expense of cornstarch (Thr and HS have identical molecular weights). Five replicate pens of 4 chicks received each of the 4 experimental diets during a 12-d feeding period (d 8–20 posthatch). Materials and Methods Assay 2. This assay sought to determine whether L-HS or a-ketobutyrate All procedures were approved by the University of Illinois Animal Care (a-KB) could spare the need for Thr in young chicks fed a Thr-deficient, and Use Committee. Four assays were conducted using male chicks from corn-peanut meal diet. Analysis of both corn and peanut meal revealed the University of Illinois Poultry Farm following the same housing and that there was no detectable free or bound HS in either ingredient. rearing procedures described by Dilger and Baker (9). Graded doses of L-Thr (0, 400, or 800 mg/kg) were added to the basal Two separate basal diets (Table 1) were formulated to evaluate the diet to produce a standard curve. As a positive control, the basal diet was Thr replacement value of L-HS. The purified and the corn-peanut meal- also supplemented with 3400 mg L-Thr/kg diet to exceed the dietary Thr basal diets were formulated to be singly deficient in Thr but were requirement for this age chick. L-HS or a-KB was added to the basal diet otherwise nutritionally complete for chicks of this age (10). Experimen- or positive control diet at concentrations isomolar to 800 mg L-Thr/kg tal diets and tap water were freely available to chicks. Body weight of diet. Each of the dietary treatments (8 total) were assigned to 4 replicate pens of 4 chicks during a 9-d feeding period (d 8–17 posthatch). Assay 3. In this assay, the Thr-sparing effect of L-HS was evaluated 1 Supported by Evonik Degussa GmbH, Hanau-Wolfgang, Germany. 2 Author disclosures: K. I. Bryant, R. N. Dilger, C. M. Parsons, and D. H. Baker, no both directly and indirectly, i.e. via contribution from L-Met (i.e. Met conflicts of interest. conversion to HS). The Thr-deficient, corn-peanut meal-basal diet was 3 Abbreviations used: AA, amino acid; CP, crude protein; HS, homoserine; a-KB, supplemented with 0 or 800 mg L-Thr/kg diet or 800 mg L-HS/kg diet a-ketobutyrate. (i.e. isomolar to 800 mg L-Thr/kg diet). Additionally, 1000 or 2000 mg * To whom correspondence should be addressed. Email: [email protected]. L-Met/kg diet (isomolar and twice isomolar that of 800 mg L-HS/kg diet, 0022-3166/08 $8.00 ã 2009 American Society for Nutrition. 1298 Manuscript received January 8, 2009. Initial review completed February 27, 2009. Revision accepted May 5, 2009. First published online May 27, 2009; doi:10.3945/jn.109.104372. TABLE 1 Composition of Thr-deficient basal diets and multiplied by 100. Four of the diets in assays 2 and 4 formed a 2 3 2 factorial arrangement of treatments. Hence, these 4 treatment diets were Corn-peanut evaluated by single degree-of-freedom contrasts to assess the main effects Purified diet meal diet of HS supplementation and Thr concentration and also the interaction. Ingredient (assay 1)1 (assays 2, 3, and 4)2 g/100 g Cornstarch 54.37 0.36 Results Corn, 8.4 g CP/100 g — 61.08 Peanut meal, 45.6 g CP/100 g — 27.50 Assay 1. Weight gain and gain:food increased (P , 0.05) when Casein, 84.8 g CP/100 g 2.50 — the Thr-deficient purified diet was supplemented with 800 mg Soy protein isolate, 82.4 g CP/100 g 4.00 — Thr/kg diet or an isomolar concentration (800 mg/kg) of L-HS AA mixture 19.563 2.264 (Table 2). The addition of 1600 mg HS/kg diet also increased Soybean oil 10.00 4.00 both gain and gain:food, but the response was no greater than Solka floc5 3.00 — that with 800 mg HS/kg. Purified mineral mix6 5.37 — Downloaded from https://academic.oup.com/jn/article/139/7/1298/4670474 by guest on 30 September 2021 Trace mineral mix6 — 0.15 Assay 2. Supplementation of the Thr-deficient corn-peanut Purified vitamin mix6 0.20 — meal diet with the first 3 doses of L-Thr resulted in linear (P , Vitamin mix6 — 0.20 0.01) responses in weight gain, food intake, and gain:food ratio Choline chloride 0.20 0.10 (Table 3). Adding 800 mg L-HS/kg to the basal diet improved P , 3 NaHCO3 1.00 0.40 ( 0.05) gain:food. Diets 1, 4, 5, and 6 represented a 2 2 Limestone — 1.40 factorial arrangement of treatments, and assessment of the Dicalcium phosphate — 2.10 interaction for these treatments revealed significance (P , 0.01) Sodium chloride — 0.40 for weight gain, food intake, and gain:food. Thus, when dietary Bacitracin premix7 — 0.05 Thr was deficient, 800 mg L-HS/kg produced a positive response, but when dietary Thr was superadequate, 800 mg L-HS/kg 1 Analyzed to contain (g/100 g diet): CP, 20.3; Thr, 0.22; Met, 0.32; cyst(e)ine, 0.20. depressed growth performance (Fig. 1). The addition of 686 mg 2 Analyzed to contain (g/100 g diet): CP, 19.0; Thr, 0.46; Met, 0.42; cyst(e)ine, 0.38. 3 Provided (g/100 g diet): L-Arg, 0.95; L-His, 0.33; L-Lys×HCl, 1.14; DL-Met, 0.20; a-KB/kg, isomolar to 800 mg HS/kg, did not affect growth L-cystine, 0.15; L-Phe, 0.50; L-Tyr, 0.45; L-Trp, 0.15; L-Leu, 1.00; L-Ile, 0.60; L-Val, 0.69; performance of chicks fed the Thr-deficient basal diet or the diet Gly, 1.00; L-Pro, 0.40; and L-Glu, 12.00. containing surfeit Thr. 4 Provided (g/100 g diet): L-Lys×HCl, 1.00; DL-Met, 0.20; L-cystine, 0.17; L-Val, 0.20; The gain:food ratio of chicks fed diets 1, 2, and 3 was used to L-Ile, 0.23; L-Arg, 0.06; L-Trp, 0.07; and Gly, 0.33. r 2 5 FS & D Corp., Urbana, OH.
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