On the activation of the canine pepsinogens.

Acidification induces a conversion of canine pepsinogens by a sequential mechanism to the active pepsins. Activation in the presence of pepstatin, which strongly inhibits the pepsins but does not prevent the first step of activation, allows the isolation of the peptide released in this first step. This peptide inhibits the milk clotting activity of canine and also porcine pepsin. Canine pepsins obtained in the absence of pepstatin were characterized by amino acid composition, molecular weight, and activity against hemoglobin and milk and compared with those of other mammalian pepsins.