title: Alkaline cleavage of disulfide bonds in the black-eyed pea trypsin and chymotrypsin inhibitor.
abstract: The rate of production of thiol groups by alkaline cleavage of disulfide bonds in the black-eyed pea (Vigna unguiculata) trypsin and chymotrypsin inhibitor (BTCI) was determined from thiol quantitation with 5, 5'-dithiobis-(2-nitrobenzoic acid), and increase in absorption at 240 nm. Rate constants were estimated at pH's 12.8, 13.0, 13.5, and 25 degrees C. At pH 13.0, the second-order rate constant was obtained as a function of temperature. The energy of activation was Ea = 10.7 kcal/mole, while the change in activation free energy was delta G not equal to = 21.6 kcal/mole. The results obtained fit the hydrolysis mechanism, in which S-S split occurs through a nucleophilic attack of a hydroxide ion on the disulfide bond. Urea (8M), unexpectedly, showed an effect of attenuation on the hydrolysis rate of disulfide bonds in BTCI.
mesh_terms: D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D002918:Chymotrypsin / Q000037:antagonists & inhibitors*; D004220:Disulfides; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010940:Plant Proteins; D012639:Seeds; D014361:Trypsin Inhibitors
chemical_list: D004220:Disulfides; D010940:Plant Proteins; D014361:Trypsin Inhibitors; C042736:trypsin, chymotrypsin inhibitor, black-eyed pea; D002918:Chymotrypsin