TY - JOUR
T1 - The influence of a free α-ammonium group in the substrate upon trypsin-catalyzed transesterification
AU - Del Castillo, Luz M.
AU - Dávila, Gloria
AU - Dorantes, Lidia
AU - Oliver, Carmen
AU - Ibarra, Roberto
AU - Castañeda-Agulló, M.
PY - 1969/11/4
Y1 - 1969/11/4
N2 - 1. 1. By comparison of rates, measured by using titration, of trypsin-catalyzed hydrolysis of either l-arginine methyl ester (AME) or l-lysine methyl ester (LME) with those determined by paper chromatography analysis, it was possible to ascertain that pKa of the α-ammonium group of both esters differs by about -1.8 units from that of the respective free amino acids. 2. 2. In aqueous alcohol solutions, the logarithm of the ratio of concentrations of products of alcoholysis to hydrolysis at a given time shows a linear relationship with the logarithm of the ratio of ionized to un-ionized species of substrate α-ammonium group. 3. 3. The ratio l-lysine ethyl ester (LEE):lysine also decreases with temperature, an effect which at least partially might be accounted for in terms of a decreased ionization of substrate α-ammonium group. 4. 4. The conclusion can be reached that k4 > k3 (the deacylation rate constant in alcoholysis is larger than the corresponding one in hydrolysis). Hence, the addition of alcohol exerts a driving effect on the reaction. Besides this effect, alcohols also accelerate the reaction by a dielectric constant effect similar to that produced by acetone on the trypsin-catalyzed hydrolysis of LME or to those observed with various solvents in the trypsin-catalyzed hydrolyses of α-N-substituted substrates.
AB - 1. 1. By comparison of rates, measured by using titration, of trypsin-catalyzed hydrolysis of either l-arginine methyl ester (AME) or l-lysine methyl ester (LME) with those determined by paper chromatography analysis, it was possible to ascertain that pKa of the α-ammonium group of both esters differs by about -1.8 units from that of the respective free amino acids. 2. 2. In aqueous alcohol solutions, the logarithm of the ratio of concentrations of products of alcoholysis to hydrolysis at a given time shows a linear relationship with the logarithm of the ratio of ionized to un-ionized species of substrate α-ammonium group. 3. 3. The ratio l-lysine ethyl ester (LEE):lysine also decreases with temperature, an effect which at least partially might be accounted for in terms of a decreased ionization of substrate α-ammonium group. 4. 4. The conclusion can be reached that k4 > k3 (the deacylation rate constant in alcoholysis is larger than the corresponding one in hydrolysis). Hence, the addition of alcohol exerts a driving effect on the reaction. Besides this effect, alcohols also accelerate the reaction by a dielectric constant effect similar to that produced by acetone on the trypsin-catalyzed hydrolysis of LME or to those observed with various solvents in the trypsin-catalyzed hydrolyses of α-N-substituted substrates.
UR - http://www.scopus.com/inward/record.url?scp=0014664018&partnerID=8YFLogxK
U2 - 10.1016/0005-2744(69)90254-X
DO - 10.1016/0005-2744(69)90254-X
M3 - Artículo
C2 - 5354266
AN - SCOPUS:0014664018
SN - 0005-2744
VL - 191
SP - 354
EP - 361
JO - BBA - Enzymology
JF - BBA - Enzymology
IS - 2
ER -