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.

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.

The Specificity of Penicillopepsin

1971 ◽  
Vol 49 (10) ◽  
pp. 1134-1149 ◽  
Author(s):  
G. Mains ◽  
Miho Takahashi ◽  
J. Šodek ◽  
T. Hofmann
Keyword(s):  
Amino Acid ◽  
Glutamic Acid ◽  
Ph Dependence ◽  
Random Copolymer ◽  
The Other ◽  
High Rate ◽  
Hydrophobic Amino Acid ◽  
Peptide Bonds ◽  
Hydrolysis Of ◽  
Very High

The specificity of penicillopepsin was investigated with a number of different substrates. In agreement with earlier work (1), no action was observed on di- and tripeptide and ester substrates. However, the pepsin substrate carbobenzoxyglycylglycylphenylalanylphenylalanine 3-(4-pyridyl)propyl-1 ester was hydrolyzed between the two phenylalanine residues. No cleavage of homopolymers of glycine, alanine, and glutamic acid and the random copolymer of glutamic acid and tyrosine was observed. Polymers of lysine, lysine and tyrosine (2:1), and lysine, glutamic acid, and tyrosine (13:20:1) were, however, hydrolyzed giving mainly tripeptides to pentapeptides. Polylysine hydrolysis showed a pH dependence centering about a group of pK between 3 and 4. In glucagon and the S-sulfo B-chain of insulin, penicillopepsin hydrolyzed the same peptide bonds as the other acidic proteases, including pepsin and rennin, with very few exceptions. There are, however, distinct differences between the action of penicillopepsin and that of other proteases of low specificity. Peptide bonds which have a hydrophobic amino acid in the P1′ position (as defined by Berger and Schechter, Ref. 2) are preferentially cleaved by penicillopepsin. A kinetic study of the hydrolysis of bovine serum albumin showed very high rate constants for the initial cleavages. The present study shows the requirement for an extended binding site in penicillopepsin.

scholarly journals The mechanism of catalysis and the inhibition of the Bacillus cereus zinc-dependent β-lactamase

1998 ◽  
Vol 331 (3) ◽  
pp. 703-711 ◽  
Author(s):  
Sakina BOUNAGA ◽  
Andrew P. LAWS ◽  
Moreno GALLENI ◽  
Michael I. PAGE
Keyword(s):  
Ph Dependence ◽  
Bound Water ◽  
Acid Catalyst ◽  
Ion Concentration ◽  
Hydrogen Ion Concentration ◽  
Class B ◽  
Mechanism Of Catalysis ◽  
Solvent Isotope ◽  
Hydrolysis Of ◽  
Dianionic Form

The plot of kcat/Km against pH for the Bacillus cereus569/H β-lactamase class B catalysed hydrolysis of benzylpenicillin and cephalosporin indicates that there are three catalytically important groups, two of pKa 5.6±0.2 and one of pKa 9.5±0.2. Below pH 5 there is an inverse second-order dependence of reactivity upon hydrogen ion concentration, indicative of the requirement of two basic residues for catalysis. These are assigned to zinc(II)-bound water and Asp-90, both with a pKa of 5.6±0.2. A thiol, N-(2´-mercaptoethyl)-2-phenylacetamide, is an inhibitor of the class B enzyme with a Ki of 70 µM. The pH-dependence of Ki shows similar pH inflections to those observed in the catalysed hydrolysis of substrates. The pH-independence of Ki between pH 6 and 9 indicates that the pKa of zinc(II)-bound water must be 5.6 and not the higher pKa of 9.5. The kinetic solvent isotope effect on kcat/Km is 1.3±0.5 and that on kcat is 1.5. There is no effect on reactivity by either added zinc(II) or methanol. The possible mechanisms of action for the class B β-lactamase are discussed, and it is concluded that zinc(II) acts as a Lewis acid to stabilize the dianionic form of the tetrahedral intermediate and to provide a hydroxide-ion bound nucleophile, whereas the carboxylate anion of Asp-90 acts as a general base to form the dianion and also, presumably, as a general acid catalyst facilitating C–N bond fission.

Enzyme-assisted Extraction for Optimized Recovery of Phenolic Bioactives from Peganum hermala Leaves Using Response Surface Methodology

2018 ◽  
Vol 17 (4) ◽  
pp. 349-354
Author(s):  
Qadir Rahman ◽  
Anwar Farooq ◽  
Amjad Gilani Mazhar ◽  
Nadeem Yaqoob Muhammad ◽  
Ahmad Mukhtar
Keyword(s):  
Response Surface Methodology ◽  
Response Surface ◽  
Enzyme Concentration ◽  
Coumaric Acid ◽  
Assisted Extraction ◽  
Pre Treatment ◽  
Optimized Conditions ◽  
Enzyme Complexes ◽  
Hydrolysis Of ◽  
Central Composite

This study investigates the effect of enzyme formulations (Zympex-014, Kemzyme dry-plus and Natuzyme) on recovery of phenolics from Peganum hermala (harmal) leaves, under optimized conditions using response surface methodology. As compared to the other enzyme complexes, the yield (34 g/100g) obtained through Zympex-014-assisted extraction was higher under optimized conditions such as time (75 min), temperature (70°C), pH (6.5) and enzyme concentration (5 g/100 g) using central composite design (CCD). Effectiveness of Zympex-014 towards hydrolysis of P. hermala leaves cell wall was examined by analyzing the control and enzyme-treated leave residues using scanning electron microscope (SEM). GC/MS characterization authenticated the presence of quercetin (1.44), gallic acid (0.23), caffeic acid (0.04), cinnamic acid (0.05), m-coumaric acid (0.23) and p-coumaric acid (0.37 μg/g) as the potent phenolics in Zympex-014 based extract. It can be concluded from the findings of the current work that pre-treatment of P. hermala leaves with Zympex-014 significantly enhanced the recovery of phenolics that supports its potential uses in the nutra-pharamaceutical industry.

scholarly journals Hydrolysis of rat chylomicron acylglycerols: a kinetic model

1981 ◽  
Vol 22 (3) ◽  
pp. 506-513 ◽  
Author(s):  
D M Foster ◽  
M Berman
Keyword(s):  
Kinetic Model ◽  
Hydrolysis Of

Kinetic model of enzymatic hydrolysis of steam-exploded wheat straw

2012 ◽  
Vol 87 (2) ◽  
pp. 1280-1285 ◽  
Author(s):  
Greta Radeva ◽  
Ivo Valchev ◽  
Stoiko Petrin ◽  
Eva Valcheva ◽  
Petya Tsekova
Keyword(s):  
Enzymatic Hydrolysis ◽  
Kinetic Model ◽  
Wheat Straw ◽  
Hydrolysis Of

scholarly journals Research on hydrogen generation from rapid hydrolysis of aluminum in sodium fluoride solution

2019 ◽  
Vol 118 ◽  
pp. 03048
Author(s):  
Changchun Li ◽  
Yuxin Wu
Keyword(s):  
Hydrogen Production ◽  
Kinetic Model ◽  
Sodium Fluoride ◽  
Hydrogen Generation ◽  
Hydrogen Yield ◽  
Shrinking Core Model ◽  
Fluoride Solution ◽  
Shrinking Core ◽  
Rapid Hydrolysis ◽  
Hydrolysis Of

Hydrogen generation from rapid hydrolysis of aluminum in sodium fluoride solution was investigated through a hydrolysis experiment. Rapid and instant hydrogen yield were observed using sodium fluoride as additive. The experimental results demonstrate that the increase of temperature and the amount of additives in a certain range will boost the hydrogen production. The amount of additives outside the range only has an effect on the rapid hydrolysis of the aluminum during the initial stage, but the total amount of hydrogen produced doesn’t increased significantly. Theoretical analysis of the effects of the mixing ratio and the temperature on the hydrogen production rates were performed using the shrinking core model and the kinetic model. The shrinking core model parameter a and k indicate the film change degree of porosity and thickness and the effect of time on the diffusion coefficient. the kinetic model is verified and the activation energy confirming hydrogen yield control by a molecular diffusion process. Correspondingly, mechanisms of Al corrosion in NaF solutions under low and high alkalinity were proposed, respectively.

scholarly journals Novel activity of angiotensin-converting enzyme. Hydrolysis of cholecystokinin and gastrin analogues with release of the amidated C-terminal dipeptide

1989 ◽  
Vol 262 (1) ◽  
pp. 125-130 ◽  
Author(s):  
P Dubreuil ◽  
P Fulcrand ◽  
M Rodriguez ◽  
H Fulcrand ◽  
J Laur ◽  
...  
Keyword(s):  
Angiotensin Converting Enzyme ◽  
Chloride Ion ◽  
Peptide Bond ◽  
Major Product ◽  
Enzyme Hydrolysis ◽  
Ion Concentration ◽  
Converting Enzyme ◽  
Rabbit Lung ◽  
Hydrolysis Of

ACE (angiotensin-converting enzyme; peptidyl dipeptidase A; EC 3.4.15.1), cleaves C-terminal dipeptides from active peptides containing a free C-terminus. We investigated the hydrolysis of cholecystokinin-8 [CCK-8; Asp-Tyr(SO3H)-Met-Gly-Trp-Met-Asp-Phe-NH2] and of various gastrin analogues by purified rabbit lung ACE. Although these peptides are amidated at their C-terminal end, they were metabolized by ACE to several peptide fragments. These fragments were analysed by h.p.l.c., isolated and identified by comparison with synthetic fragments, and by amino acid analysis. The initial and major site of hydrolysis was the penultimate peptide bond, which generated a major product, the C-terminal amidated dipeptide Asp-Phe-NH2. As a secondary cleavage, ACE subsequently released di- or tri-peptides from the C-terminal end of the remaining N-terminal fragments. The cleavage of CCK-8 and gastrin analogues was inhibited by ACE inhibitors (Captopril and EDTA), but not by other enzyme inhibitors (phosphoramidon, thiorphan, bestatin etc.). Hydrolysis of [Leu15]gastrin-(14-17)-peptide [Boc (t-butoxycarbonyl)-Trp-Leu-Asp-Phe-NH2] in the presence of ACE was found to be dependent on the chloride-ion concentration. Km values for the hydrolysis of CCK-8, [Leu15]gastrin-(11-17)-peptide and Boc-[Leu15]gastrin-(14-17)-peptide at an NaCl concentration of 300 mM were respectively 115, 420 and 3280 microM, and the catalytic constants were about 33, 115 and 885 min-1. The kcat/Km for the reactions at 37 degrees C was approx. 0.28 microM-1.min-1, which is approx. 35 times less than that reported for the cleavage of angiotensin I. These results suggest that ACE might be involved in the metabolism in vivo of CCK and gastrin short fragments.

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