PAPAIN-CATALYZED HYDROLYSIS OF AND AMINO-ACID-INCORPORATION INTO BSA AND ZEIN SUBSTRATES IN LOW WATER-ORGANIC MEDIA

Papain, either modified with polyethylene glycol (PEG) or in the form of a suspended powder, was used to catalyze the digestion of protein s ubstrates in organic solvents to gain insights into protein-protein in teractions in media of this kind. Bovine serum albumin was efficiently hydrolyzed in toluene containing 1-2% added water (v/v). The extent o f proteolysis, as estimated by amino group determination, depended on the water concentration and, under the optimal condition, was 20% high er than that obtained in aqueous media using the same enzyme/substrate ratio. The highest rate of hydrolysis was obtained in the most hydrop hobic solvent, but the attachment of polyethylene glycol chains to the enzyme did not enhance the catalysis. Proteolysis in organic solvents can be said to constitute an interesting approach to the enzymatic di gestion of proteins and amino acid incorporation involved in aminolysi s. In the case of the hydrophobic protein zein, more than 10% of the p eptide bonds were hydrolyzed by PEG-papain in toluene, and in the pres ence of a potent nucleophile such as Lys-OMe or Lys-NH2 the transpepti dation reaction resulted in an increase in the lysine content of zein from 0. 15% to 3.5% and 10.4%, respectively. The use of organic media therefore provides a potentially useful approach to the enzymatic modi fication of food protein.