The Enzymatic Determination of Glutamine by Regikald M. Archibald*

Existing methods of measuring glutamine depend upon either the liberation of ammonia by mild acid hydrolysis (1) or on the fact that when heated at 100” in neutral or slightly acid solution transformation to pyrrolidonecarboxylic acid occurs with disappearance of the amino nitrogen (2) determined by the nitrous acid method (3) and disappearance of the -CH(NH2). COOH group determined by evolution of its CO2 when heated with ninhydrin (4, 5). In view of the growing interest in the physiological r61e of glutamine (5-9) it seems desirable to have available also a specific enzymatic micromethod. Krebs (9) demonstrated that the cortex of rabbit, pig, guinea pig, and sheep kidney contained an enzyme, glutaminase, which hydrolyzed glutamine to glutamic acid and ammonia, and the writer has described a preparation adapted to analytical use (10). The present paper outlines a method which uses this enzyme to determine the glutamine content of blood, plasma, and plant extracts and to assay the purity of glutamine preparations . Use of this method to assist in identifying glutamine amide nitrogen as a source of urinary ammonia has been published in a preliminary note (11). Two procedures will be described. In one, the “filtrate nesslerization procedure,” the digest is deproteinized and the ammonia is determined in the filtrate. In the other, the “distillation procedure,” the ammonia is distilled in 2rucuo and nesslerized in the distillate. The filtrate method, though less accurate and less satisfactory than the distillation method, is included since it permits approximate estimation of glutamine when the distillation apparatus is not available.