COPRECIPITATION OF AMINO ACIDS WITH TUNGSTIC ACID PRECIPITATION OF PLASMA PROTEINS

The effect of tungstic acid precipitation of plasma proteins on the nonprotein α-amino nitrogen concentration and on the recovery of added 14C-labeled amino acids was investigated. Total loss of α-amino nitrogen from the rabbit plasma was estimated to be between 10 and 23%. The major loss of α-amino nitrogen appears to be due to the loss of diamino acids; the loss of 14C-labeled arginine, histidine, and lysine ranged between 30 and 50%. Loss of neutral amino acids was for the most part very small (less than 2%) and, with the exception of threonine, not significant. Loss of glutamic acid was estimated to be 4%. The actual extent of amino acid loss was shown to depend on the relative concentration of proteins and precipitating agents and was not greatly influenced by reasonable variations in precipitating procedures. The lost amino acids are firmly bound to the precipitate and cannot be recovered even with several washes. It was concluded that most of the observed loss of α-amino nitrogen is due to binding of dibasic amino acids to a protein-tungstate complex. © 1969.