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Nitrogen Retention in Men Fed Isolated Soybean Protein Supplemented with L-Methionine, D-Methionine, N-Acetyl-L-Methionine, or Inorganic Sulfate¹

Department of Nutritional Sciences, University of California, Berkeley, California 94720

The ability of various sulfur-containing compounds to replace L-methionine (L-Met) was investigated by metabolic balance studies in man. N-acetyl-L-Methionine (AcMet), D-methionine (D-Met), and sodium sulfate (Na₂SO₄) were used to supplement a diet deficient in sulfur amino acids. The daily diet contained 4.5 g nitrogen (N) from isolated soybean protein (SB) and 4.5 g from glycine and alanine (9 g total N). SB diet was given alone or supplemented to six adult men for periods of 9 days after a standardization period with an equal N eggwhite diet, preceded by a 2-day zero N adaptation period. Supplements provided equivalent amounts of sulfur to that present in 420 mg L-Met, the amount added to SB to bring the total sulfur amino acid content to 900 mg/day. AcMet was as beneficial as L-Met in improving N balance but D-Met was not as effective as L-Met. Difference between balances obtained with L-Met and Na₂SO₄ was not significant due to large variation in response to Na₂SO₄. While addition of D-Met to SB did not result in significantly greater N retention than unsupplemented SB, Na₂SO₄ addition did cause increased N retention.

KEY WORDS: • L-methionine • D-methionine • inorganic sulfate • N-acetyl-L-methionine • isolated soybean protein • nitrogen balance study • human

¹ Supported by USPHS Grants AM 10202 and 5A02AH00095 and by a gift from Procter and Gamble. Submitted in partial fulfillment for the degree of Doctor of Philosophy in Nutrition. University of California. Berkeley. Presented in part at the 59th Annual Meeting of the Federation of American Societies for Experimental Biology, Atlantic City, N.J. (1975) Federation Proc. 34, 3776 (Abstr.).

Manuscript received 27 January 1976.

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