Isolation and characterization of proteases from Euphorbia lactea and Euphorbia lactea cristata

Latex from E. lactea yielded three homogeneous proteases, euphorbains, 1a1, 1a2 and 1a3 with Mr of 66 k, 44 k and 33 k respectively. Euphorbains 1a1 and 1a3 had unique pIs of, in order, 7.0 and 4.5, while 1a2 comprised three charged forms with pIs ranging from 5.0 to 6.4. From the latex of E. lactea cristata a single proteolytic euphorbain 1c was isolated which had an Mr of 70 000 and five pIs between 5.0 and 8.0. Euphorbains 1a1 and 1c have similar substrate specificities which are different from those of 1a2 and 1a3. Euphorbains 1a1, 1a2 and 1c are serine-centred enzymes with vital histidine residues, and the latter protease is activated by Ca2+, Mg2+ and Mn2+.