title: Reinvestigation of the reaction of chymotrypsin with N-furylacryloyltryptophan derivatives at acidic pH.
abstract: The reaction of alpha-chymotrypsin with N alpha-3-(2-furyl)acryloyl-L-tryptophan methyl ester (FA-Trp-OMe) and amide has been investigated in aqueous and dimethylsulphoxide cryosolvent solutions from pH2 to 7 and over a wide temperature range. Previous reports have suggested that an intermediate preceding the acyl-enzyme can be detected spectrophotometrically in the reaction with methyl esters of FA-Trp and FA-Tyr at low pH [Yu & Viswanatha (1969) Eur. J. Biochem. 11, 347--352), and that this intermediate is an oxazolinone [Coletti-Previero et al. (1970) FEBS Lett. 11, 213--217]. We show that the previous interpretations of the time-dependent spectral changes were incorrect, and that the only detected intermediate is the acyl-enzyme. This may be isolated by gel filtration at pH less than 2.5, 1 degree C, owing to its relative stability. The pH-dependence of the rates of acylation and deacylation from pH 8.5 to 2.0 are consistent with a single ionization of pK congruent to 7.0 in both aqueous and cryosolvent solutions.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D002918:Chymotrypsin; D006863:Hydrogen-Ion Concentration; D012997:Solvents; D013053:Spectrophotometry; D013696:Temperature; D014364:Tryptophan / Q000031:analogs & derivatives*
chemical_list: D012997:Solvents; D014364:Tryptophan; D002918:Chymotrypsin