Characterization of peptic inhibitory activity associated with sulfated glycoprotein isolated from gastric mucosa

Sulfated glycoproteins were extracted and purified from porcine stomach mucous scraping. Four sulfated glycoprotein fractions were separated and subsequently purified. These compounds always accompanied the apparent peptic inhibitory activity and consisted of 15-18% (w/w) protein. The carbohydrate portions contained an equimolar ratio of galactose and hexosamine (mainly glucosamine), together with lesser amounts of fucose and sialic acid. The sulfate content of the above fractions was 2-9% (w/w) of the total sulfated glycoprotein. The mode of inhibition of the sulfated glycoproteins to peptic activity was investigated and suggested that there was binding of the sulfated glycoproteins to the substrate of pepsin, making the substrate resistant to peptic activity. The sulfated glycoproteins neither bound pepsin at pH 1.8 nor inhibited the hydrolysis of a synthetic dipeptide substrate of pepsin. Desulfation of the sulfated glycoproteins resulted in the loss of both the inhibitory activity and the precipitate formation. The precipitation curve for sulfated glycoprotein and porcine serum albumin showed that both bound in varying proportions and suggests that both components are multivalent in this precipitate formation.