Cucumisin like protease from the sarcocarp of Benincasa hispida var. Ryukyu

A protease has been purified from the sarcocarp of Benincasa hispida (Thunb.) Cogn. var. Ryukyu by two steps of chromatography. Its M(r) was estimated by SDS-PAGE to be about 67,000. The enzyme was strongly inhibited by diisopropyl fluorophosphate, but not by EDTA and cysteine protease inhibitors. The substrate having alanine at the position of P1 was the best among the Ala-Ala-Pro-X-pNAs (X = Ala, Lys, Phe, Glu, and diaminopropionic acid (Dap)). The N-terminal sequence of the first 33 residues was determined and 25 of the residues agreed with that of cucumisin [EC 3.4.21.25], a protease from the sarcocarp of melon fruit (Cucumis melo L. var. Prince). The results indicated that the B. hispida protease is a cucumisin like serine protease.