Chemical mechanism of β-glucosidase from Trichoderma reesei QM 9414. pH-dependence of kinetic parameters

1992 ◽  
Vol 283 (3) ◽  
pp. 679-682 ◽  
Author(s):  
I de la Mata ◽  
P Estrada ◽  
R Macarrón ◽  
J M Dominguez ◽  
M P Castillón ◽  
...  
Keyword(s):  
Kinetic Parameters ◽  
Trichoderma Reesei ◽  
Carboxy Group ◽  
Ph Dependence ◽  
Competitive Inhibitor ◽  
Chemical Mechanism ◽  
Histidine Residue ◽  
Activity Temperature ◽  
Beta Glucosidase ◽  
Mechanism Of The Reaction

The variation of kinetic parameters of beta-glucosidase from Trichoderma reesei QM 9414 with pH was used to gain information about the chemical mechanism of the reaction catalysed by this enzyme. The pH-dependence of Vmax. and Vmax./Km for p-nitrophenyl beta-D-glucopyranoside showed that a group with a pK value of 4.3 must be unprotonated and a group with a pK value of 5.9 must be protonated for activity. Temperature and solvent-perturbation studies indicated that these groups are a histidine residue and a carboxy group respectively. Profiles of pKi for maltose as competitive inhibitor showed that binding is prevented when a group on the enzyme with a pK value of 4.5 becomes protonated.

scholarly journals Chemical mechanism of D-amino acid oxidase from Rhodotorula gracilis: pH dependence of kinetic parameters

1998 ◽  
Vol 330 (1) ◽  
pp. 311-314 ◽  
Author(s):  
F. RAMÓN ◽  
M. P. CASTILLÓN ◽  
I. DE LA MATA ◽  
C. ACEBAL
Keyword(s):  
Amino Acid ◽  
Kinetic Parameters ◽  
Ph Dependence ◽  
Competitive Inhibitor ◽  
Chemical Mechanism ◽  
Acid Oxidase ◽  
Protonation State ◽  
Amino Acid Oxidase ◽  
Basic Group ◽  
Rhodotorula Gracilis

The variation of kinetic parameters of D-amino acid oxidase from Rhodotorula gracilis with pH was used to gain information about the chemical mechanism of the oxidation of D-amino acids catalysed by this flavoenzyme. D-Alanine was the substrate used. The pH dependence of Vmax and Vmax/Km for alanine as substrate showed that a group with a pK value of 6.26-7.95 (pK1) must be unprotonated and a group with a pK of 10.8-9.90 (pK2) must be protonated for activity. The lower pK value corresponded to a group on the enzyme involved in catalysis and whose protonation state was not important for binding. The higher pK value was assumed to be the amino group of the substrate. Profiles of pKi for D-aspartate as competitive inhibitor showed that binding is prevented when a group on the enzyme with a pK value of 8.4 becomes unprotonated; this basic group was not detected in Vmax/Km profiles suggesting its involvement in binding of the β-carboxylic group of the inhibitor.

Chemical mechanism of β-xylosidase from Trichoderma reesei QM 9414: pH-dependence of kinetic parameters

Biochimie ◽  
2001 ◽  
Vol 83 (10) ◽  
pp. 961-967 ◽  
Author(s):  
María Gómez ◽  
Pablo Isorna ◽  
Marta Rojo ◽  
Pilar Estrada
Keyword(s):  
Kinetic Parameters ◽  
Trichoderma Reesei ◽  
Ph Dependence ◽  
Chemical Mechanism

Chemical mechanism of penicillin V acylase from Streptomyces lavendulae: pH-dependence of kinetic parameters

2001 ◽  
Vol 16 (1) ◽  
pp. 33-41 ◽  
Author(s):  
Raquel Torres-Guzmán ◽  
Isabel de la Mata ◽  
Jesús Torres-Bacete ◽  
Miguel Arroyo ◽  
Marı́a Pilar Castillón ◽  
...  
Keyword(s):  
Kinetic Parameters ◽  
Ph Dependence ◽  
Chemical Mechanism ◽  
Penicillin V ◽  
Streptomyces Lavendulae ◽  
Penicillin V Acylase

scholarly journals Mechanism of the reaction catalysed by cytosolic 5′-nucleotidase/phosphotransferase: formation of a phosphorylated intermediate

1996 ◽  
Vol 317 (3) ◽  
pp. 797-801 ◽  
Author(s):  
Cristina BAIOCCHI ◽  
Rossana PESI ◽  
Marcella CAMICI ◽  
Roichi ITOH ◽  
Maria GRAZIA TOZZI
Keyword(s):  
Reaction Mechanism ◽  
Kinetic Parameters ◽  
Acid Treatment ◽  
Histidine Residue ◽  
Thiol Oxidation ◽  
Photo Oxidation ◽  
Calf Thymus ◽  
Hydrolysis Of ◽  
Mechanism Of The Reaction

Cytosolic 5´-nucleotidase preferentially catalysing the hydrolysis of IMP, GMP and their deoxy derivatives, and endowed with phosphotransferase activity, was purified from calf thymus and its reaction mechanism was studied. In the presence of [32P]IMP, ATP and MgCl2, a covalent enzyme–phosphate intermediate was trapped by mixing with an SDS solution. Heat or acid treatment of the enzyme before incubation with radiolabelled substrate prevented formation of the intermediate. Furthermore, on the basis of studies on the kinetic parameters of the enzyme as function of pH, and of experiments on thiol oxidation and photo-oxidation, we suggest the involvement of cysteine and histidine residue(s) in the reaction mechanism.

scholarly journals Chemical mechanism of lysophosphatidylcholine: lysophosphatidylcholine acyltransferase from rabbit lung. pH-dependence of kinetic parameters

1990 ◽  
Vol 270 (3) ◽  
pp. 761-764 ◽  
Author(s):  
J Pérez-Gil ◽  
J Martín ◽  
C Acebal ◽  
R Arche
Keyword(s):  
Kinetic Model ◽  
Ph Dependence ◽  
Chemical Mechanism ◽  
Histidine Residue ◽  
Rabbit Lung ◽  
Mechanism Of Catalysis ◽  
Enzyme Complexes ◽  
Hydrolysis Of ◽  
Enthalpy Of Ionization ◽  
Very High

Lysophosphatidylcholine: lysophosphatidylcholine acyltransferase is an enzyme that catalyses two reactions: hydrolysis of lysophosphatidylcholine and transacylation between two molecules of lysophosphatidylcholine to give disaturated phosphatidylcholine. Following the kinetic model previously proposed for this enzyme [Martín, Pérez-Gil, Acebal & Arche (1990) Biochem. J. 266, 47-53], the values of essential pK values in free enzyme and substrate-enzyme complexes have now been determined. The chemical mechanism of catalysis was dependent on the deprotonation of a histidine residue with pK about 5.7. This result was supported by the perturbation of pK values by addition of organic solvent. Very high and exothermic enthalpy of ionization was measured, indicating that a conformational re-arrangement in the enzyme accompanies the ionization of the essential histidine residue. These results, as well as the results from previous studies, enabled the proposal of a chemical mechanism for the enzymic reactions catalysed by lysophosphatidylcholine: lysophosphatidylcholine acyltransferase from rabbit lung.

α-Retaining glucosyl transfer catalysed by trehalose phosphorylase from Schizophyllum commune: mechanistic evidence obtained from steady-state kinetic studies with substrate analogues and inhibitors

2001 ◽  
Vol 360 (3) ◽  
pp. 727-736 ◽  
Author(s):  
Bernd NIDETZKY ◽  
Christian EIS
Keyword(s):  
Steady State ◽  
Transition State ◽  
Schizophyllum Commune ◽  
Catalytic Efficiency ◽  
Kinetic Studies ◽  
Competitive Inhibitor ◽  
Chemical Mechanism ◽  
Steady State Kinetic ◽  
State Kinetic ◽  
Trehalose Phosphorylase

Fungal trehalose phosphorylase is classified as a family 4 glucosyltransferase that catalyses the reversible phosphorolysis of α,α-trehalose with net retention of anomeric configuration. Glucosyl transfer to and from phosphate takes place by the partly rate-limiting interconversion of ternary enzyme–substrate complexes formed from binary enzyme–phosphate and enzyme–α-d-glucopyranosyl phosphate adducts respectively. To advance a model of the chemical mechanism of trehalose phosphorylase, we performed a steady-state kinetic study with the purified enzyme from the basidiomycete fungus Schizophyllum commune by using alternative substrates, inhibitors and combinations thereof in pairs as specific probes of substrate-binding recognition and transition-state structure. Orthovanadate is a competitive inhibitor against phosphate and α-d-glucopyranosyl phosphate, and binds 3×104-fold tighter (Ki≈ 1μM) than phosphate. Structural alterations of d-glucose at C-2 and O-5 are tolerated by the enzyme at subsite +1. They lead to parallel effects of approximately the same magnitude (slope = 1.14; r2 = 0.98) on the reciprocal catalytic efficiency for reverse glucosyl transfer [log (Km/kcat)] and the apparent affinity of orthovanadate determined in the presence of the respective glucosyl acceptor (log Ki). An adduct of orthovanadate and the nucleophile/leaving group bound at subsite +1 is therefore the true inhibitor and displays partial transition state analogy. Isofagomine binds to subsite −1 in the enzyme–phosphate complex with a dissociation constant of 56μM and inhibits trehalose phosphorylase at least 20-fold better than 1-deoxynojirimycin. The specificity of the reversible azasugars inhibitors would be explained if a positive charge developed on C-1 rather than O-5 in the proposed glucosyl cation-like transition state of the reaction. The results are discussed in the context of α-retaining glucosyltransferase mechanisms that occur with and without a β-glucosyl enzyme intermediate.

scholarly journals Mechanism of d-fructose isomerization by Arthrobacterd-xylose isomerase

1992 ◽  
Vol 283 (1) ◽  
pp. 223-233 ◽  
Author(s):  
M Rangarajan ◽  
B S Hartley
Keyword(s):  
Ring Opening ◽  
Ph Dependence ◽  
Xylose Isomerase ◽  
Competitive Inhibitor ◽  
Apparent Dissociation Constant ◽  
Ph Values ◽  
Rate Limiting Step ◽  
Competitive Inhibitors ◽  
Rate Limiting ◽  
Very High

The mechanism of D-fructose isomerization by Arthrobacter D-xylose isomerase suggested from X-ray-crystallographic studies was tested by detailed kinetic analysis of the enzyme with various metal ions at different pH values and temperatures. At D-fructose concentrations used in commercial processes Mg2+ is the best activator with an apparent dissociation constant of 63 microM; Co2+ and Mn2+ bind more strongly (apparent Kd 20 microM and 10 microM respectively) but give less activity (45% and 8% respectively). Ca2+ is a strict competitive inhibitor versus Mg2+ (Ki 3 microM) or Co2+ (Ki 105 microM). The kinetics show a compulsory order of binding; Co2+ binds first to Site 2 and then to Site 1; then D-fructose binds at Site 1. At normal concentrations Mg2+ binds at Site 1, then D-fructose and then Mg2+ at Site 2. At very high Mg2+ concentrations (greater than 10 mM) the order is Mg2+ at Site 1, Mg2+ at Site 2, then D-fructose. The turnover rate (kcat.) is controlled by ionization of a residue with apparent pKa at 30 degrees C of 6.0 +/- 0.07 (Mg2+) or 5.3 +/- 0.08 (Co2+) and delta H = 23.5 kJ/mol. This appears to be His-219, which is co-ordinated to M[2]; protonation destroys isomerization by displacing M[2]; Co2+ binds more strongly at Site 2 than Mg2+, so competes more strongly against H+. The inhibition constant (Ki) for the two competitive inhibitors 5-thio-alpha-D-glucopyranose and D-sorbitol is invariant with pH, but Km(app.) in the Mg[1]-enzyme is controlled by ionization of a group with pKa 6.8 +/- 0.07 and delta H = 27 kJ/mol, which appears to be His-53. This shows that Km(app.) is a complex constant that includes the rate of the ring-opening step catalysed by His-53, which explains the pH-dependence. In the Mg[1]Mg[2]-enzyme or Co[1]Co[2]-enzyme, the pKa is lower (6.2 +/- 0.1 or 5.6 +/- 0.08) because of the extra adjacent cation. Hence the results fit the previously proposed pathway, but show that the mechanisms differ for Mg2+ and Co2+ and that the rate-limiting step is isomerization and not ring-opening as previously postulated.

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