The thiol proteinases from the latex of Carica papaya L. I. Fractionation, purification and preliminary characterization.

Three thiol proteinases, namely papain, chymopapain and proteinase omega were purified to homogeneity from the latex of Carica papaya L. During the purification procedure, the thiol function of the cysteinyl residues were protected either as mixed disulfides with cysteamine or 2-thiopyridone or as S-sulphenylthiosulfate derivative or after blocking with p-chloromercuribenzoic acid. In marked contrast with earlier publications, chymopapain also was found to be a monothiol proteinase as papain and proteinase omega. The active sites of chymopapain and proteinase omega could not be distinguished from that of papain neither by the analysis of the pH dependence of kcat/Km nor by the examination of the pH dependence of the fluorescence emission spectra.