Amino Acids, Including Asparagine and Glutamine, in Plasma and Urine of Normal Human Subjects

The use of lithium citrate buffer systems for the analyses of acidic and neutral amino acids in plasma and urine was tested and found superior to the usually employed sodium citrate buffer systems. The lithium systems have the advantage of resolving asparagine and glutamine without loss of resolution of other acidic and neutral amino acids. Normal levels of these amides in plasma and urine were established, and the relative contributions of the aspartic and glutamic acids, their amides, and unknown conjugates (peptides?) to the total measurable acids in protein-free filtrates after hydrolysis were determined. The general pattern of excretion of amino acids in urine collected for 4 hr from fasting individuals was shown to be quite similar to the pattern found in 24-hr urines collected from nonfasting subjects.