The Determination of Glycine in Proteins* by A. R. Patton

Very few methods for the determination of glycine have been published. Fischer’s method (1) suffers from the usual inadequacies of isolation methods : requiring a large amount of protein, being extremely long and tedious, and yielding only minimal values. Other isolation methods which have been proposed present equally great difficulties. Zimmerman (2) has described a color t.est whereby a violet color is produced through the interaction of o-phthalic dialdehyde and glycine. This test’ is, however, not specific, since colors are produced with certain other amino acids. Recently Klein and Linser (3) have modified Zimmerman’s test, and their modification appears to be specific and quantitative for glycine. If the o-phthalic dialdehyde reagent is added to a solution of glycine which has been made slightly alkaline and, after standing for a time, this mixture is acidified, a dark green color and precipitate are formed. The precipitate dissolves if a little alcohol is added. Certain other amino acids, if present in the solution, produce red or violet colors. However, the green glycine compound can be quantitatively extracted by chloroform, the colored compounds formed by the other amino acids being left behind in the aqueous solution. Klein and Linser have shown that colors are produced by glycine, tryptophane, cystine, arginine, alanine, asparagine, and ammonium salts, but that only the colors produced by glycine, tryptophane, and the ammonium ion are extracted by chloroform. They found that the following substances produce no color: valine, leucine, tyrosine, serine, phenyl-