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The properties of carboxyl proteinase which was contained is Poria cocos (Schw.) Wolf were investigated by means of the purification with 0.65 ammonium sulfate saturation, DEAE-cellulose sad Sephadex G-75 gel filtration. This enzyme was found to hydrolyze only peptide bond between glutamyl-L-tyrosine of carbobenzoxy-L-glutamyl-L-tyrosine among the synthetic substrates of carbobenzoxy-L-glutamyl-L-tyrosine, hippuryl-L-phenylalanine and hippuryl-L-arginine. This enzyme was inhibited by Zn^(+2), Fe^(+2), Ca^(+2), CN^(-1), P₂O_7^(-1) ions, but stimulated by Hg^(+2) ion. Also, this enzyme was inhibited by organic compounds such as L-lysine, L-phenylalanine, hippuryl-L-phenylalaniae, diazoacetyl-DL-norleucine methyl ester (DAN) and 1.2-epoxy-3-(P-nitrophenoxy)propane(EPNP). In particular, the activity was inhibited by L-lysine till 20 minutes of preincubation time rapidly, and by DAN in the presence of Cu^(+2) ion more rapidly after 30 minutes than DAN in the absence of Cu^(+2) ion. L-Lysine was found to be a competitive inhibitor and its K_i value was determined to be 0.12 mmole by Dixon plot.
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