Identification of Monkey Lung Procathepsin d‐II as a Pepsinogen‐C‐Like Acid Protease Zymogen

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Abstract
Procathepsin D-II (MW = 37,500) was purified from Japanese monkey lung at pH 7.0, and was shown to be converted to the active form, cathepsin D-II(MW = 33,000) via an intermediate (MW = 35,500) upon treatment at pH 3.0 and 14.degree. C. Procathepsin D-II was the inactive precursor of cathepsin D-II based on the following results: the former was inactive toward heat-denaturated casein at pH 5.4 whereas the latter was active; the former was not activated by diazoacetyl-DL-norleucine methyl ester in the presence of Cu2+ ion at pH 6.0 whereas the latter was inactivated rapidly under the same conditions; and the former had no affinity to pepstatin-Sepharose between pH 5 and 7 whereas the latter was adsorbed to it. With a rabbit antiserum against procathepsin D-II, cathepsin D-II, pepsinogen C and pepsin C of Japanese monkey gave a single precipitin line which fused completely with each other on agarose plate. On the other hand, cathepsin D-I purified from the monkey lung, and pepsinogens A (I, II, III-1, III-2 and III-3) obtained from the monkey gastric mucosa failed to precipitate with the antiserum. With the antiserum against the monkey pepsinogen C, the same results were obtained. Further, procathepsin D-II and pepsinogen C had the same amino-terminal amino acid sequence, Ala-Val-Val-Lys-Val-Pro-Leu-Lys-Lys-Phe-Lys. All these results indicate a strong similarity of procathepsin D-II and cathepsin D-II to pepsinogen C and pepsin C, respectively.