A. Ferjancicbiagini et al., PAPAIN-CATALYZED HYDROLYSIS OF AND AMINO-ACID-INCORPORATION INTO BSA AND ZEIN SUBSTRATES IN LOW WATER-ORGANIC MEDIA, Journal of agricultural and food chemistry, 41(7), 1993, pp. 1152-1157
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.