Gastric Juice I. Studies on the Proteins of the Gastric Juice of Humans

The studies to be reported were undertaken with the idea of throwing more light on the proteins of the gastric juice. It has been found that they can be precipitated by tungstic acid at pH 3.5 and that, although heating coagulated a protein, there remained in solution a heat-uncoagulable substance which gave a positive biuret reaction. Interest in the subject was stimulated by the investigations on the non-protein nitrogen constituents of the gastric juice (1). As a result of the investigations to be reported, it has been found that there are present in the normal human gastric juice, in addition to the proteins of the mucus, two protein-like bodies. The first has been called gastroglobulin and is precipitated by magnesium sulfate at one-half saturation (further saturation does not increase the yield of protein) by an acetic acid and acetone mixture, and by heat. It does not contain a carbohydrate. Although in its chemical analysis it resembles a mucoprotein, it appears to be a distinct substance. It has been crystallized from various media. The second protein-like material is precipitated from the acetic acid-acetone filtrate and from the heated gastric juice, after globulin has been removed, by tungstic acid at pH 3.5. When this second precipitate is hydrolyzed in 2 per cent HZS04, a compound is liberated which exhibits typical carbohydrate properties; namely, it reduces alkaline copper sulfate and forms osazone-like