Effect of storage at 20 degrees C on the concentration of amino acids in plasma.

Amino acids were determined in whole and deproteinized plasma from six subjects, before and after storage at -20 degrees C over a period of four weeks. When the native plasma was stored the following changes were observed after four weeks (fractions, mean +/- SEM): increase of glutamic acid (to 1.30 +/- 0.11), decrease of glutamine (to 0.91 +/- 0.03), half-cystine (to 0.24 +/- 0.09) and arginine (to 0.94 +/- 0.02). In stored deproteinized plasma, only glutamine decreased slightly (to 0.96 +/- 0.02) in four weeks. The concentration of 22 other amino acids remained unchanged irrespective of the type of storage.