Conjugated amino acids in plasma of patients with uremia.

In patients with renal insufficiency, the elevated plasma nonprotein nitrogen cannot be accounted for solely by the rise in the urea nitrogen (2). It is known that other nitrogenous materials such as creatinine and uric acid contribute to this elevation. Since free amino acids also contribute to the nonprotein, nonurea nitrogen of plasma, several investigators have determined the amino acid composition of plasma from both normal subjects and patients with uremia. They have shown that in uremia, concentrations of the individual plasma are normal or that such alterations in concentrations as exist are slight and probably insignificant (3-7). In addition, the total a-amino nitrogen in plasma of patients with uremia remains approximately normal (3-10). However, studies in which deproteinized plasma was hydrolyzed revealed that some anmino acids are variably increased in concentration (34). These findings suggested the presence of one or more amino acid conjugates in the plasma of patients with uremia. The investigations described in this paper were undertaken to characterize further the amino acid conjugates in the plasma of patients with uremia. The general plan of the study consisted of measurement of a-amino nitrogen in deproteinized plasma of normal subjects, and of patients with uremia before and after hydrolysis. By means of dialysis through cellophane, rough indications were obtained of the molecular size of conjugates containing nitrogen. By chromatographic separation and serial fraction collections, the sources of conjugate nitrogen were concentrated. At-