PEPSINOGENS AND PEPSINS FROM HOUSE MUSK SHREW, SUNCUS-MURINUS - PURIFICATION, CHARACTERIZATION, DETERMINATION OF THE AMINO-ACID-SEQUENCES OF THE ACTIVATION SEGMENTS, AND ANALYSIS OF PROTEOLYTIC SPECIFICITIES

Three pepsinogens, namely, pepsinogens A, C-l, and C-2, were purified from gastric mucosa of adult house mush shrew (Suncus murinus) by conv entional chromatographic and gel filtration procedures, The molecular masses were 40, 39, and 41 kDa for pepsinogens A, C-l, and C-2, respec tively. Pepsinogen C-2 contains an Asn-linked carbohydrate chain(s) of about 2 kDa. Each pepsinogen was converted to pepsin through an inter mediate farm under acidic conditions, By NH2-terminal sequence analysi s of these protein species, the amino acid sequences of activation seg ments (proparts) of pepsinogens A and C-l were determined to be LYKVPL VKKKSLRQNLIENGLLKDFLAKHNVNPASKYFPTE and KVTKVTLKKFKSIRENLREQGLLEDFLKTN HYDPAQKYHFGDF, respectively. The similarity of these two sequences is nearly 50%. Each pepsin cleaved preferentially peptide bonds between h ydrophobic and aromatic amino acids, or bonds on either side of these amino acids. Although each activation segment had several sites suscep tible to pepsin action, activation proceeded by limited cleavages of t he segment, presumably due to the steric inflexibility of the segment in native pepsinogen. The activity of pepsin A was inhibited completel y 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-l and C-2.