scholarly journals Imidazole Catalyses in Aqueous Systems. III. Formation of the Catalyst-Substrate Complex in the Hydrolysis of a Phenyl Ester Catalyzed by a Naphthylimidazole Derivative

1970 ◽  
Vol 43 (4) ◽  
pp. 1109-1119 ◽  
Author(s):  
Toyoki Kunitake ◽  
Seiji Shinkai ◽  
Chuji Aso
Keyword(s):  
Aqueous Systems ◽  
Phenyl Ester ◽  
Substrate Complex ◽  
Hydrolysis Of

scholarly journals Interactions of tervalent lanthanide ions with bacterial collagenase (clostridiopeptidase A)

1981 ◽  
Vol 195 (3) ◽  
pp. 677-684 ◽  
Author(s):  
Christopher H. Evans
Keyword(s):  
Ionic Radius ◽  
Substrate Inhibition ◽  
Volume Ratio ◽  
Binding Pocket ◽  
Lanthanide Ions ◽  
Ionic Radii ◽  
Apparent Dissociation Constant ◽  
Substrate Complex ◽  
Bacterial Collagenase ◽  
Hydrolysis Of

Tervalent cations of the lanthanide (rare-earth) elements reversibly inhibit bacterial collagenase (clostridiopeptidase A; EC 3.4.24.3). Sm3+, whose ionic radius is closest to that of Ca2+, is the most effective inhibitor, completely suppressing clostridiopeptidase activity at a concentration of 100μm in the presence of 5mm-Ca2+. Er3+ and Lu3+, which both have ionic radii smaller than either Ca2+ or Sm3+, inhibit less efficiently, and La3+, which is slightly larger than Ca2+ or Sm3+, inhibits only weakly. These findings indicate a closely fitting, stereospecific, Ca2+-binding pocket in clostridiopeptidase, which excludes ions that are only slightly larger than Ca2+ [ionic radius 0.099nm (0.99 Ȧ)]. By contrast, trypsin, an enzyme whose activity does not depend on Ca2+, requires lanthanide concentrations 50–100-fold greater for inhibition. Furthermore, the relative efficiency of inhibition of trypsin by lanthanides increases as the lanthanide ions become smaller and the charge/volume ratio increases. At a concentration of 50μm, Sm3+ lowers the apparent Km for the hydrolysis of Pz-peptide by clostridiopeptidase from 5.4mm to 0.37mm and the apparent Vmax. from 0.29 Wünsch–Heidrich unit to 0.018 unit. Thus Sm3+ enhances the affinity of this enzyme for its substrate; inhibition of hydrolysis of Pz-peptide may result from the excessive stability of the enzyme–Sm3+–substrate complex. Inhibition by Sm3+ is competitive with regard to Ca2+. The apparent dissociation constant, Kd, of Ca2+ is 0.27mm, where the Ki for Sm3+ is 12μm. Clostridiopeptidase is more thermolabile in the absence of Ca2+. With Sm3+, thermoinactivation of the enzyme at 53°C or 60°C is initially accelerated, but then becomes retarded as heating continues. Lanthanide ions bind to gelatin and collagen. In so doing, they appear to protect these substrates from lysis by clostridiopeptidase through mechanisms additional to supplanting Ca2+ at its binding site on the enzyme. Collagen and gelatin sequester sufficient lanthanide ions to gain partial protection from clostridiopeptidase in the absence of an extraneous source of these inhibitors.

Effect of Modifiers on the Hydrolysis of Basic and Neutral Peptides by Carboxypeptidase B

1975 ◽  
Vol 53 (7) ◽  
pp. 747-757 ◽  
Author(s):  
Graham J. Moore ◽  
N. Leo Benoiton
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Kinetic Behavior ◽  
Carboxypeptidase A ◽  
Phenyllactic Acid ◽  
Carboxypeptidase B ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
Basic Peptides ◽  
Hydrolysis Of

The initial rates of hydrolysis of Bz-Gly-Lys and Bz-Gly-Phe by carboxypeptidase B (CPB) are increased in the presence of the modifiers β-phenylpropionic acid, cyclohexanol, Bz-Gly, and Bz-Gly-Gly. The hydrolysis of the tripeptide Bz-Gly-Gly-Phe is also activated by Bz-Gly and Bz-Gly-Gly, but none of these modifiers activate the hydrolysis of Bz-Gly-Gly-Lys, Z-Leu-Ala-Phe, or Bz-Gly-phenyllactic acid by CPB. All modifiers except cyclohexanol display inhibitory modes of binding when present in high concentration.Examination of Lineweaver–Burk plots in the presence of fixed concentrations of Bz-Gly has shown that activation of the hydrolysis of neutral and basic peptides by CPB, as reflected in the values of the extrapolated parameters, Km(app) and keat, occurs by different mechanisms. For Bz-Gly-Gly-Phe, activation occurs because the enzyme–modifier complex has a higher affinity than the free enzyme for the substrate, whereas activation of the hydrolysis of Bz-Gly-Lys derives from an increase in the rate of breakdown of the enzyme–substrate complex to give products.Cyclohexanol differs from Bz-Gly and Bz-Gly-Gly in that it displays no inhibitory mode of binding with any of the substrates examined, activates only the hydrolysis of dipeptides by CPB, and has a greater effect on the hydrolysis of the basic dipeptide than on the neutral dipeptide. Moreover, when Bz-Gly-Lys is the substrate, cyclohexanol activates its hydrolysis by CPB by increasing both the enzyme–substrate binding affinity and the rate of the catalytic step, an effect different from that observed when Bz-Gly is the modifier.The anomalous kinetic behavior of CPB is remarkably similar to that of carboxypeptidase A, and is a good indication that both enzymes have very similar structures in and around their respective active sites. A binding site for activator molecules down the cleft of the active site is proposed for CPB to explain the observed kinetic behavior.

Hydrolysis of Zinc Ion and Solubility of Zinc Oxide in High-Temperature Aqueous Systems

1997 ◽  
Vol 127 (3) ◽  
pp. 292-299 ◽  
Author(s):  
Yukiko Hanzawa ◽  
Daisuke Hiroishi ◽  
Chihiro Matsuura ◽  
Kenkichi Ishigure ◽  
Masashi Nagao ◽  
...  
Keyword(s):  
Zinc Oxide ◽  
High Temperature ◽  
Zinc Ion ◽  
Aqueous Systems ◽  
Hydrolysis Of

scholarly journals Photodegradation and Hydrolysis of Chlorpyrifos in Aqueous Systems

2014 ◽  
Vol 33 (4) ◽  
pp. 553 ◽  
Author(s):  
JE Ukpebor ◽  
S Ikpeni ◽  
NC Ejiogu ◽  
EE Ukpebor
Keyword(s):  
Aqueous Systems ◽  
Hydrolysis Of

Human cholinesterases

2020 ◽  
pp. 63-120
Author(s):  
Sergey Varfolomeev ◽  
Bella Grigorenko ◽  
Sofya Lushchekina ◽  
Alexander Nemuchin
Keyword(s):  
Active Site ◽  
The Body ◽  
Polymorphic Modification ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
Mechanism Of Hydrolysis ◽  
The Central Nervous System ◽  
The Stability ◽  
Hydrolysis Of ◽  
Enzyme Reactivity

The work is devoted to modeling the elementary stages of the hydrolysis reaction in the active site of enzymes belonging to the class of cholinesterases — acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). The study allowed to describe at the molecular level the effect of the polymorphic modification of BChE, causing serious physiolog ical consequences. Cholinesterase plays a crucial role in the human body. AChE is one of the key enzymes of the central nervous system, and BChE performs protective functions in the body. According to the results of calculations using the combined method of quantum and molecular mechanics (KM/MM), the mechanism of the hydrolysis of the native acetylcholine substrate in the AChE active center was detailed. For a series of ester substrates, a method for estimation of dependence of the enzyme reactivity on the structure of the substrate has been developed. The mechanism of hydrolysis of the muscle relaxant of succininylcholine BChE and the effect of the Asp70Gly polymorph on it were studied. Using various computer simulation methods, the stability of the enzyme-substrate complex of two enzyme variants with succinylcholine was studied.

scholarly journals Changes in u(VI) SPeciation Upon Sorption onto Montmorillonite from Aqueous and Organic Solutions

1991 ◽  
Vol 257 ◽  
Author(s):  
Catherine Chisholm-Brause ◽  
Steven D. Conradson ◽  
P. Gary Eller ◽  
David E. Morris
Keyword(s):  
Oxidation State ◽  
Aqueous Systems ◽  
X Ray ◽  
Ph Values ◽  
Uranium Oxidation ◽  
Organic Solutions ◽  
X Ray Absorption ◽  
Hydrolysis Of ◽  
Uranium Species ◽  
Lines Of Evidence

ABSTRACTThe speciation of UO22+ and UO22+/ TBP mixtures has been investigated in solution and intercalated with the reference smectite clay SAz-1 using x-ray absorption, Raman, andluminescence spectroscopies. Neither aquated UO22+ nor its TBP complex undergoes any detectable changes in uranium oxidation state on intercalation. Further, at the pH values employed in this work, there is no evidence for hydrolysis of the uranium species to generate dimeric or higher order uranium oligomers. However, we do find indications that the structures of the solution complexes are altered on intercalation, particularly for the UO22+TBP system and for more dilute UO22+/aqueous systems. In addition, several lines of evidence suggest that, at the loading levels used in this study, the uranyl species is interacting with two or more spectroscopically distinguishable sites on SAz-1.

scholarly journals Role of Sulfated Tyrosines of Thyroglobulin in Thyroid Hormonosynthesis

Endocrinology ◽  
2005 ◽  
Vol 146 (11) ◽  
pp. 4834-4843 ◽  
Author(s):  
Marie-Christine Nlend ◽  
David M. Cauvi ◽  
Nicole Venot ◽  
Odile Chabaud
Keyword(s):  
Amino Acid ◽  
Coupling Reaction ◽  
Short Life ◽  
Hormone Synthesis ◽  
Amino Acid Peptide ◽  
Substrate Complex ◽  
Enzyme Substrate ◽  
Saturation Binding ◽  
Hydrolysis Of

Our previous studies showed that sulfated tyrosines (Tyr-S) are involved in thyroid hormone synthesis and that Tyr5, the main hormonogenic site of thyroglobulin (Tg), is sulfated. In the present paper, we studied the role of Tyr-S in the formation and activity of the peroxidase-Tg complex. Results show that noniodinated 35SO3-Tg specifically binds (Kd = 1.758 μm) to immobilized lactoperoxidase (LPO) via Tyr-S linkage by using saturation binding and competition experiments. We found that NIFEY-S, a 15-amino acid peptide corresponding to the NH2-end sequence of Tg and containing the hormonogenic acceptor Tyr5-S, was a better competitor than cholecystokinin and Tyr-S. 35SO3-Tg, iodinated without peroxidase, bound to LPO with a Kd (1.668 μm) similar to that of noniodinated Tg, suggesting that 1) its binding occurs via Tyr-S linkage and 2) Tyr-S requires peroxidase to be iodinated, whereas nonsulfated Tyr does not. Iodination of NIFEY-S with [125I]iodide showed that Tyr5-S iodination increased with LPO concentration, whereas iodination of a nonsulfated peptide containing the donor Tyr130 was barely dependent on LPO concentration. Enzymatic hydrolysis of iodinated Tg or NIFEY-S showed that the amounts of sulfated iodotyrosines also depended on LPO amount. Sulfated iodotyrosines were detectable in the enzyme-substrate complex, suggesting they have a short life before the coupling reaction occurs. Our data suggest that after Tyr-S binding to peroxidase where it is iodinated, the sulfate group is removed, releasing an iodophenoxy anion available for coupling with an iodotyrosine donor.

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