TY - JOUR
T1 - Binding of Competitive Inhibitors to S-Chymotrypsin in the Alkaline pH Region. Competitive Inhibition Kinetics and Proton-Uptake Measurements
AU - Valenzuela, Pablo
AU - Bender, Myron L.
PY - 1970/6/1
Y1 - 1970/6/1
N2 - The binding of the three competitive inhibitors benzyl alcohol, tryptophol, and N-acetyl-D-tryptophanamide to α- and δ-chymotrypsins was studied over the pH range 7 to 11 by competitive inhibition kinetics using N-furyl-acryloyl-L-tryptophan methyl ester as substrate. The results indicate that the binding of these inhibitors to δ-chymotrypsin exhibits a pH dependence significantly different from the pH dependence obtained with α-chymotrypsin. Analysis of K, vs. pH profiles for the interaction of benzyl alcohol, tryptophol, and N-acetyl-D-tryptophanamide with δ-chymotrypsin indicates that the pKa of an ionizing group of the enzyme (9.2, 9.5, and 9.2, respectively) is shifted to a pKa of 10.0, 10.1, and 9.8, respectively, in the enzyme-inhibitor complex. This behavior differs from that of α-chymotrypsin, where, in agreement with previous reports, the binding of the three inhibitors was found to be strictly dependent on the ionization of a group in the enzyme with a pKa of 9.0 that apparently shifts upon binding of inhibitor to a value of 11.5 or higher. The proton uptake that accompanies the binding of the three inhibitors to δ-chymotrypsin was also measured as a function of pH. A good agreement between the measured proton uptake and the predicted values from the corresponding pKa shifts was found. It is concluded that the different behavior of α- and δ-chymotrypsins at high pH reflects a difference in the binding abilities of the enzymes. The present hypotheses regarding the conformation and activity of α-chymotrypsin at alkaline pH are discussed in the light of this particular behavior of δ-chymotrypsin.
AB - The binding of the three competitive inhibitors benzyl alcohol, tryptophol, and N-acetyl-D-tryptophanamide to α- and δ-chymotrypsins was studied over the pH range 7 to 11 by competitive inhibition kinetics using N-furyl-acryloyl-L-tryptophan methyl ester as substrate. The results indicate that the binding of these inhibitors to δ-chymotrypsin exhibits a pH dependence significantly different from the pH dependence obtained with α-chymotrypsin. Analysis of K, vs. pH profiles for the interaction of benzyl alcohol, tryptophol, and N-acetyl-D-tryptophanamide with δ-chymotrypsin indicates that the pKa of an ionizing group of the enzyme (9.2, 9.5, and 9.2, respectively) is shifted to a pKa of 10.0, 10.1, and 9.8, respectively, in the enzyme-inhibitor complex. This behavior differs from that of α-chymotrypsin, where, in agreement with previous reports, the binding of the three inhibitors was found to be strictly dependent on the ionization of a group in the enzyme with a pKa of 9.0 that apparently shifts upon binding of inhibitor to a value of 11.5 or higher. The proton uptake that accompanies the binding of the three inhibitors to δ-chymotrypsin was also measured as a function of pH. A good agreement between the measured proton uptake and the predicted values from the corresponding pKa shifts was found. It is concluded that the different behavior of α- and δ-chymotrypsins at high pH reflects a difference in the binding abilities of the enzymes. The present hypotheses regarding the conformation and activity of α-chymotrypsin at alkaline pH are discussed in the light of this particular behavior of δ-chymotrypsin.
UR - http://www.scopus.com/inward/record.url?scp=0014938162&partnerID=8YFLogxK
U2 - 10.1021/bi00814a008
DO - 10.1021/bi00814a008
M3 - Article
C2 - 5423263
AN - SCOPUS:0014938162
VL - 9
SP - 2440
EP - 2446
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 12
ER -