The Thiol Proteinases from the Latex ofCarica papayaL. IV. Proteolytic Specificities of Chymopapain and Papaya Proteinase Ω Determined by Digestion of α-Globin Chains

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Abstract
The proteolytic specificities of chymopapain and papaya proteinase .OMEGA. were investigated by using the .alpha.-chains of manatee and mole haemoglobin, whose primary structures are known, as substrates. The resulting peptides from each enzymatic cleavage were isolated by gel filtration on Sephadex G-25 followed by reversed-phase HPLC of the separated peaks and, in some cases, further purified by preparative thin-layer electrophoresis. The purified peptides were then identified on the basis of their amino-acid composition. The proteolytic specificities of chymopapain and papaya proteinase .OMEGA. deduced from the experimental cleavage patterns, are compared to that of papain. As in the case of papain, the specificity-determining factor is the amino-acid residue of the substrate that will be bound in subsite S2 (the next but one from the scissible bond). Aromatic residues in this position, preferred by papain, are not important for chymopapain and papaya proteinase .OMEGA.. Cleavages preferentially occur when S2 is occupied by leucine, valine or threonine. For chymopapain, proline in position S2 also causes cleavage.