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Effect of Level and Proportion of Methionine and Cystine on Plasma Amino Acids of Young Rats^1,2,

Foods and Nutrition Department, Purdue University, Lafayette, Indiana 47907

Amino acids in the plasma of young rats were measured to determine whether they would reflect dietary intakes of two different proportions of sulfur from methionine (M) and cystine (C), 70M:30C or 30M:70C in experiment 1. Higher concentrations of methionine, lysine and alanine (P < 0.01), and of isoleucine, valine and a-amino-n-butyric acid (P < 0.05) were present in the plasma of the animals fed 70M:30C, whereas threonine and taurine were depressed (P < 0.01) as compared with those rats fed the 30M:70C ratio. In experiment 2 the 70M:30C ratio was tested at four levels of total sulfur, 0.144, 0.122, 0.100 and 0.078%, with three levels of added inorganic sulfur, 0.044, 0.022 and 0.000%. Concentrations of threonine and urea decreased and those of cystine and taurine increased (P < 0.01) in the plasma as organic sulfur was raised. Only the levels of serine (P < 0.01), proline and asparagine-glutamine (P < 0.05) were affected by inorganic sulfur.

KEY WORDS: • plasma amino acids • methionine • cystine • inorganic sulfate

¹ From Purdue University Agricultural Experiment Station and School of Home Economics, Department of Foods and Nutrition, Lafayette, Indiana 47907. Journal paper 4552.

² The data were taken from a thesis submitted by Martha H. Byington in partial fulfillment of the requirement for the degree of Doctor of Philosophy at Purdue University and the research was supported in part by a fellowship under National Defense Education Act — Title IV.

³ Present address: 2243 Harcourt Dr., Cleveland, Ohio 44106.

Manuscript received 23 September 1971.