The synthetic peptides AC-Glu-Phe-Phe (NO2)-Arg-amide (peptide VP) and
AC-Ile-Glu-Phe-Phe (NO2)Arg-amide (peptide VIP) are more readily hydr
olyzed by human pepsin in gastric juice of patients of gastritis than
those of duodenal ulcer and normal subjects. The kinetic parameters su
ggest that S-3 subsite of the enzyme plays a role in the elevation of
enzyme activity in gastric disease.