A Method for the Assay of Commercial Gastric Mucin

Abstract

Following the introduction by Fogelson 1 of gastric mucin therapy for gastro-duodenal ulcerative disease, a method for the assay of commercial preparations became desirable.

The commercial gastric mucin is prepared by following the customary procedure for commercial pepsin, in which the mucin dough is separated from the pepsin by precipitation at its iso-electric point. It is then purified by repeated washing with 70% alcohol; 2 mixed with required base, and diluted with peptone to decrease the viscosity to a practical state for administration to patients. Although it is the opinion of Hurst 3 that “mucus differs from other proteins in the extreme slowness with which it undergoes peptic digestion…,” nitrogen and reduction values to be presented for commercial mucin suggest the possibility of a partial digestion, when compared with values obtained for gastric mucin by Webster and Komarov. 4 This phase of the subject is being investigated.

Commercial samples were found to vary greatly as to viscosity, acid combining power, sulphur, nitrogen, and mucoitin content. Methods were therefore sought by which mucin could be separated from the commercial diluents and contaminants before assay. For this purpose we have used an additional peptic digestion followed by precipitation with 70% alcohol. By weighing the precipitated material, comparative values for the mucin content of the samples may be obtained. Our data shows this procedure to give a product with characteristic N₂ content and reduction values. Details of the procedure are as follows: Dissolve 1 gm. commercial mucin and 0.1 gm. pepsin (Wilson's 10,000 units/gram) together in 25 ml. of 0.25% (0.068 N) HC1. This strength acid was found to give a pH approximating 2 with most samples. Digest in the incubator at 37°C. over night, then pipette 10 cc. aliquot samples into weighed 50 cc. centrifuge tubes, and add 28 ml. of 95% alcohol. The contents of the tubes are thoroughly mixed and centrifuged at high speed until the precipitate is well packed (5-10 min.).