scholarly journals The active site and mechanism of action of bovine pancreatic ribonuclease. 3. The pH-dependence of the kinetic parameters for the hydrolysis of cytidine 2′,3′-phosphate

1962 ◽  
Vol 85 (1) ◽  
pp. 127-134 ◽  
Author(s):  
DG HERRIES ◽  
AP MATHIAS ◽  
BR RABIN
Keyword(s):  
Kinetic Parameters ◽  
Mechanism Of Action ◽  
Active Site ◽  
Ph Dependence ◽  
Pancreatic Ribonuclease ◽  
Hydrolysis Of

Jack bean urease (EC 3.5.1.5). V. On the mechanism of action of urease on urea, formamide, acetamide, N-methylurea, and related compounds

1980 ◽  
Vol 58 (12) ◽  
pp. 1335-1344 ◽  
Author(s):  
Nicholas E. Dixon ◽  
Peter W. Riddles ◽  
Carlo Gazzola ◽  
Robert L. Blakeley ◽  
Burt Zerner
Keyword(s):  
Enzymatic Hydrolysis ◽  
Mechanism Of Action ◽  
Active Site ◽  
Ph Dependence ◽  
Jack Bean Urease ◽  
Nickel Ion ◽  
Jack Bean ◽  
First Time ◽  
Hydrolysis Of ◽  
Hydrolysis Of Urea

Acetamide and N-methylurea have been shown for the first time to be substrates for jack bean urease. In the enzymatic hydrolysis of urea, formamide, acetamide, and N-methylurea at pH 7.0 and 38 °C, kcat has the values 5870, 85, 0.55, and 0.075 s−1, respectively. The urease-catalyzed hydrolysis of all these substrates involves the active-site nickel ion(s). Enzymatic hydrolysis of the following compounds could not be detected: phenyl formate, p-nitroformanilide, trifluoroacetamide, p-nitrophenyl carbamate, thiourea, and O-methylisouronium ion. In the enzymatic hydrolysis of urea, the pH dependence of kcat between pH 3.4 and 7.8 indicates that at least two prototropic forms are active. Enzymatic hydrolysis of urea in the presence of methanol gave no detectable methyl carbamate. A mechanism of action for urease is proposed which involves initially an O-bonded complex between urea and an active-site Ni2+ ion and subsequently an O-bonded carbamato–enzyme intermediate.

The Active Site and Mechanism of Action of Bovine Pancreatic Ribonuclease

Nature ◽  
1961 ◽  
Vol 190 (4778) ◽  
pp. 781-784 ◽  
Author(s):  
DOROTHY FINDLY ◽  
D. G. HERRIES ◽  
A. P. MATHIAS ◽  
B. R. RABIN ◽  
C. A. ROSS
Keyword(s):  
Mechanism Of Action ◽  
Active Site ◽  
Pancreatic Ribonuclease

scholarly journals Catalysis by acetylcholinesterase in two-hydronic-reactive states. Integrity of deuterium oxide effects and hydron inventories

1992 ◽  
Vol 285 (2) ◽  
pp. 451-460 ◽  
Author(s):  
E Salih
Keyword(s):  
Kinetic Parameters ◽  
Conformational Change ◽  
Rate Constants ◽  
Literature Abstract ◽  
Deuterium Oxide ◽  
Ph Dependence ◽  
Reversible Inhibitor ◽  
Induced Fit ◽  
Rate Limiting ◽  
Hydrolysis Of

Low 2H2O effects (1.0-1.5) for the parameter k(cat.)/Km in the hydrolysis of various substrates by acetylcholinesterase (AcChE) is due to normal 2H2O effects (1.8-2.8) for the parameter k(cat.) and 2H2O effects of 1.0-2.5 for the parameter Km. The analyses and interpretations of 2H2O effects in the literature utilizing the parameter k(cat.)/Km, which led to the proposal of ‘isotope insensitivity’ of the catalytic steps and the hypothesis of a rate-limiting substrate-induced-fit conformational change, are incorrect. Since k(cat.) is the only parameter that can represent the hydron-transfer step solely, the 2H2O effect can most appropriately be evaluated by using this parameter. Calculations and comparison of acylation (k+2) and deacylation (k+3) rate constants show that acylation is rate-determining for most substrates and the improved binding -0.84 to -2.09 kJ/mol (-0.2 to -0.5 kcal/mol) in 2H2O obscures the normal 2H2O effect on k(cat.) when the ratio k(cat.)/Km is utilized. Consistent with this, measurements of the inhibition constant (KI(com.)) for a reversible inhibitor, phenyltrimethylammonium, lead to KI(com.)H2O = 39 +/- 3 microM and KI(com.)2H2O = 24.5 +/- 3.5 microM, an 2H2O effect of 1.59 +/- 0.26. pH-dependence of k(cat.) in 2H2O is subject to variability of the pK(app.) values, as evaluated in terms of the two-hydronic-reactive states (EH and EH2) of AcChE, and is due to an uneven decrease in 2H2O of the kinetic parameters k'cat. for the EH2 state relative to k(cat.) for the EH state, thus leading to variable shifts in pK(app.) values of between 0.5 and 1.2 pH units for this parameter. The observed pH-independent limiting rate constants for k(cat.)/Km(app.) are made to vary between 0.5 and 1.0 in 2H2O by effects on kinetic parameters for the EH2 state, k'cat./K'm varying between 0.2 and 0.7 relative to the EH state, with k(cat.)/Km varying between 0.4 and 1.0. The effects observed on k(cat.)/Km(app.) are ultimately the result of variable effects of 2H2O on k'cat. and K'm for the EH2 state relative to k(cat.) and Km for the EH state of AcChE. These effects are responsible for the variable shifts and more than 0.5 pH unit of the pK(app.) values in 2H2O for pH-k(cat.)/Km profiles. The upward-bowing hydron inventories for k(cat.)/Km are the result of linear hydron inventories for k(cat.) and downward-bowing on Km and are not due to the rate-limiting substrate-induced fit process as claimed in the literature.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals The susceptibility of N-acetyl-S-alkyl- and N-acetyl-S-aryl-cysteine ethyl esters to chymotryptic hydrolysis

1970 ◽  
Vol 118 (4) ◽  
pp. 553-556 ◽  
Author(s):  
A. P. Damoglou ◽  
H. Lindley ◽  
I. W. Stapleton
Keyword(s):  
Kinetic Parameters ◽  
Mechanism Of Action ◽  
Ethyl Esters ◽  
Hydrolysis Of

1. The preparation of the ethyl esters of some N-acetyl-S-alkyl- and N-acetyl-S-aryl-cysteine derivatives is described. 2. Kinetic parameters for the hydrolysis of these esters by chymotrypsin are reported. 3. The results are discussed in terms of the mechanism of action of chymotrypsin and also with reference to the possible application to sequence studies of cysteine-containing proteins.

scholarly journals The active site and mechanism of action of bovine pancreatic ribonuclease. 7. The catalytic mechanism

1962 ◽  
Vol 85 (1) ◽  
pp. 152-153 ◽  
Author(s):  
D Findlay ◽  
DG Herries ◽  
AP Mathias ◽  
BR Rabin ◽  
CA Ross
Keyword(s):  
Mechanism Of Action ◽  
Active Site ◽  
Catalytic Mechanism ◽  
Pancreatic Ribonuclease

scholarly journals pH dependence of kinetic parameters of pepsin, rhizopuspepsin, and their active-site hydrogen bond mutants.

1992 ◽  
Vol 267 (26) ◽  
pp. 18413-18418
Author(s):  
Y Lin ◽  
M Fusek ◽  
X Lin ◽  
J.A. Hartsuck ◽  
F.J. Kezdy ◽  
...  
Keyword(s):  
Hydrogen Bond ◽  
Kinetic Parameters ◽  
Active Site ◽  
Ph Dependence
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