Reaction of Folin's Reagent with Proteins and Biuret Compounds in Presence of Cupric Ion

Abstract

In an earlier paper1 the writer noted that traces of copper sulfate increased the blue color obtained by treating such proteins as pepsin or gelatin with Folin's phenol reagent.It has now been found that a number of organic substances reduce the Folin's phenol reagent only if a small amount of cupric ion is present. These same substances also show a positive biuret reaction.The copper-phenol values in Table I represent the amount of color per milligram of substance produced as a result of adding m/1300 copper sulfate to the solution under examination with the phenol reagent. One obtains this value from the difference in color values produced with and without copper ion. For many substances no color is produced in the absence of copper but most proteins contain tyrosine and tryptophane and must, therefore, be analyzed with and without cupric ion. No attempt has been made to determine whether each of the substances in Table I produces a blue color exactly in proportion to its concentration. With leucyl-glyc...