Papain, an endolytic cysteine protease (EC: 3.4.22.2), from Carica papaya latex has been chemically modified using succinic anhydride. This reagent reacts with the amino group of the lysine residues in the enzyme, thereby changing its net charge from positive to negative. The resultant enzyme had its optimum pH shifted from pH 6 to 8 and there was no change in the temperature optima of 70degreesC. The modified papain had a specific activity of about 62.8 IU mg(-1) of protein at pH 8.0 at 30degreesC, whereas for the native enzyme it was 46.57 IU mg(-1) under same conditions. Stability of the modified papain was further increased by entrapping in alginate/starch beads. The immobilized papain retained its activity even after six cycles of hydrolysis. The wet beads, when dried at 50 +/- 2degreesC, increased the storage stability of the immobilized enzyme. The succinylated papain is active in various organic solvents and hence can be successfully used in biotransformations as well as being used as a proteolytic component in detergents. (C) 2004 Society of Chemical Industry.