Effect of Certain Factors on Nitrogen Retention and Lysine Requirements of Adult Human Subjects

Glycine, glutamic acid and diammonium citrate were tested as sources of supplementary nitrogen for young adult human subjects who consumed a diet containing cereals and purified essential amino acids. Lysine intake was either 850 or 900 mg, and quantities of other essential amino acids also exceeded minimal requirements. The daily intake of nitrogen was 9.0 gm, of which approximately one-half was provided by a supplementary source. In the first experiment, glycine and diammonium citrate were tested alone and in combination with each other and with glutamic acid. In the second experiment, glycine was tested alone, with glutamic acid, and with glutamic acid and diammonium citrate. Mean nitrogen balances varied from + 0.08 to + 0.62 gm. Nitrogen retention was significantly higher when glycine and glutamic acid were used together (+ 0.62 gm) than when diammonium citrate was administered alone (+ 0.08 gm). Other combinations of glycine, diammonium citrate and glutamic acid did not differ significantly from each other or from glycine alone. Urinary excretion of free α-amino nitrogen and of glycine was related directly to glycine intake. Urinary lysine was not influenced by the source of supplementary nitrogen.