title: The reactions of alpha-chymotrypsin and related proteins with ester substrates in non-aqueous solvents.
abstract: 1. The reactivity of alpha-chymotrypsin toward p-nitrophenylacetate has been studied in dimethylformamide, dimethylsulfoxide, formamide and methylacetamide. p-Nitrophenol is liberated in dimethylsulfoxide only. 2. The reactions of alpha-chymotrypsin in dimethylsulfoxide are characterized by the same kinetic and equilibrium constants with either the p-nitrophenyl esters of straight chain carboxylic acids (from acetic to n-caprylic) or with the "specific substrate", N-carbobenzoxy-DL-phenylalanine p-nitrophenyl ester. This signifies that reactions of alpha-chymotrypsin in dimethylsulfoxide, unlike those in aqueous medium, have no specificity toward su-strate structure. 3. The stoichiometry of alpha-chymotrypsin reactions in dimethylsulfoxide was shown to be about five moles of substrate per mole of enzyme. After attaining this stoichiometry, the reaction is completed. 4. Optical rotatory dispersion spectra indicate that in non-aqueous media alpha-chymotrypsin undergoes a large conformational transition which results in a random coil. 5. Chymotrypsinogen, trypsin, trysinogen, lysozyme and serum albumin react with p-nitrophenylacetate in dimethylsulfoxide at rates which are approximately equal to those of alpha-chymotrypsin. Thus, the "activity" of alpha-chymotrypsin in dimethylsulfoxide toward p-nitrophenylacetate does not differ from the "activity" of other proteins, some of which are not even hydrolytic enzymes.
mesh_terms: D001665:Binding Sites; D002918:Chymotrypsin / Q000378:metabolism*; D004121:Dimethyl Sulfoxide; D007700:Kinetics; D008433:Mathematics; D009596:Nitrophenols; D011485:Protein Binding; D012997:Solvents; D013329:Structure-Activity Relationship; D014357:Trypsin / Q000378:metabolism
chemical_list: D009596:Nitrophenols; D012997:Solvents; D002918:Chymotrypsin; D014357:Trypsin; D004121:Dimethyl Sulfoxide