1997 Volume 121 Issue 6 Pages 1010-1017
Three pepsinogens, namely, pepsinogens A, C-1, and C-2, were purified from gastric mucosa of adult house musk shrew (Suncus murinus) by conventional chromatographic and gel filtration procedures. The molecular masses were 40, 39, and 41 kDa for pepsinogens A, C-1, and C-2, respectively. Pepsinogen C-2 contains an Asn-linked carbohydrate chain(s) of about 2 kDa. Each pepsinogen was converted to pepsin through an intermediate form under acidic conditions. By NH2-terminal sequence analysis of these protein species, the amino acid sequences of activation segments (proparts) of pepsinogen A and C-1 were determined to be LYKVPLVKKKSLRQNLIENGLLKDFLAKHNVNPASKYFPTE and KVTKVTLKKF-KSIRENLREQGLLEDFLKTNHYDPAQKYHFGDF, respectively. The similarity of these two sequences is nearly 50%. Each pepsin cleaved preferentially peptide bonds between hydrophobic and aromatic amino acids, or bonds on either side of these amino acids. Although each activation segment had several sites susceptible to pepsin action, activation proceeded by limited cleavages of the segment, presumably due to the steric inflexibility of the segment in native pepsinogen. The activity of pepsin A was inhibited completely in the presence of a more than equimolar amount of pepstatin, while a hundred-molar excess amount of pepstatin was needed for the complete inhibition of the activity of pepsins C-1 and C-2.
