Porcine gastric mucin: effect of carbohydrate moieties on susceptility to pancreatic proteases

ABSTRACT

Digestion of porcine gastric, containing an average of one hexasaccharide per three amino acids, with a mixture of glycosidases gave a partial loss of carbohydrate and an increase in turbidity. The original mucin was completely resistant to digestion, but the carbohydrate-depleted mucin was degraded by pancreatic proteases. Amino acid analyses of the glycosidase-treated mucin indicate that it different from the original mucin. These results indicate that the closely spaced oligosaccharide chains on gastrointestinal mucins may be responsible both for maintaining their solubility and for their resistance to digestion by glycosidases and proteases. Since the carbohydrate-depleted mucin is much more susceptible to proteolysis than the mucin-glycoprotein subunit, bacterial glycosidases rather than proteases are apparently limiting in mucin digestion