Effect of Level and Proportion of Methionine and Cystine on Plasma Amino Acids of Young Rats

Abstract

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.