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Plasma Free Amino Acids in Children Consuming Lupin Protein with and without Methionine Supplementation¹

William C. MacLean, Jr.^*,,,, George G. Graham^*,,,, Robert P. Placko^* and Guillermo Lopez De Romaña

^* Gastroenterology and Nutrition Unit, Department of Pediatrics, School of Medicine Division of Human Nutrition, Department of International Health, School of Hygiene and Public Health, The Johns Hopkins University, Baltimore, MD 21205 Instituto de Investigación Nutricional, Apartado 55, Miraflores (Lima), Peru

Plasma free amino acids were measured in the fasting state and 3 and 4 hours postprandially in children after 9 days consumption of diets in which lupin provided all of 6.4–6.7% protein kcal, either with supplementation of 2% (grams/gram protein) DL-methionine (L + Met, n = 9) or with an isonitrogenous amount of urea (L + U, n = 10). Fasting concentration of total amino acids (TAA) and of essential amino acids (TEAA) and the TEAA:TAA molar ratio did not differ between diets. Fasting Met concentration (15 ± 4 µmol/liter) and the Met:TEAA ratio (0.021 ± 0.005) were markedly depressed after 9 days of L + U. Supplementation with Met caused an expected increase of Met concentration (25 ± 6 µmol/liter) and the Met:TEAA molar ratio (0.039 ± 0.007) and a profound decrease of Thr concentration (119 ± 28 to 77 ± 22 µmol/liter) and Thr:TEAA (0.165 ± 0.027 to 0.124 ± 0.028). Postprandially after L + U, Met and Met:TEAA did not change from their low fasting values. After L + Met, Met and Met:TEAA increased significantly relative to fasting values. Threonine concentration increased but the Thr:TEAA ratio decreased significantly (0.124 ± 0.028 to 0.111 ± 0.027). These studies confirm Met as the first-limiting amino acid in lupin protein and suggest that Thr becomes limiting when Met is provided in adequate amounts.

KEY WORDS: • lupin • amino acid • lupin + methionine

¹ Supported by a grant from the German Agency for Technical Cooperation (G. T. Z.) and in part by Contract ta-C-1286 from the Agency for International Development, U.S. Department of State.

Manuscript received 8 June 1982.

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