The thiol proteinases from the latex of Carica papaya L. II. The primary structure of proteinase omega.

The complete primary structure of the proteinase omega isolated from the latex of the Carica papaya fruits is given. The polypeptide chain contains 216 amino-acid residues, the alignment of which was deduced from sequence analyses of the native enzyme, the tryptic, chymotryptic, peptic and thermolysinolytic peptides and facilitated due to the considerable degree of homology with papain and actinidin. The location of the three disulfide bridges could be established with the help of peptic and thermolysinolytic fragments. Proteinase omega shares 148 identical amino-acid residues (68.5%) with papain and 108 ones (50%) with actinidin, including the three disulfide bridges and the free cysteine residue required for activity, as well as most of the other amino-acid residues involved in the catalytic mechanism and two thirds of the glycine residues which are of structural significance. The homology with other cysteine proteinases of different origin is discussed.