Anionic and cationic dog trypsin. Isolation and partial characterization.

One anionic and one cationic dog trypsin have been identified in dog pancreatic juice and isolated. The dog pancreatic juice contained 1.4 mg/ml of anionic trypsinogen and 1.0 mg/ml of cationic trypsinogen, respectively. The conversion of the trypsinogens to active enzymes is autocatalytic with the formation of active enzymes with higher isoelectric points than the zymogens. Although the amino acid compositions of the two trypsins were similar to those of other mammalian trypsins, a significant difference in content of acidic and basic amino acids, respectively, was found between the two dog trypsins. A high extent of cross-inhibition of the dog trypsins and of bovine trypsin by antibodies to each of the dog trypsins indicated immunological cross-reaction between the various trypsins despite lack of demonstrable cross-precipitation in gels. The calculated s(20,w)0 value for both dog trypsins was 3.3 S. The Km value of anionic trypsin for benzoyl-D,L-arginine-p-nitroanilide' HCl was found to be similar to that of cationic trypsin and to that of bovine cationic trypsin. Soybean trypsin inhibitor, chicken ovomucoid, porcine and bovine secretory inhibitors are potent inhibitors of anionic and cationic dog trypsin.