Time-dependent inhibition of γ-aminobutyric acid aminotransferase, by 3-hydroxybenzylhydrazine

Lightcap, Eric S.; Hopkins, Mark H.; Olson, Gregory T.; Silverman, Richard B.

doi:10.1016/0968-0896(95)00070-w

Cited by 4 publications

(11 citation statements)

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“…[28] More recently, there have been a number of attempts to increase the potency of inhibitors of PLP-dependent enzymes that contain a reactive hydrazide. Ejim et al .…”

Section: Discussionmentioning

confidence: 99%

“…[9] The reactivity of hydrazines and hydrazides with PLP-dependent transaminases has been known for decades, [27] and the kinetics of inhibition were studied in detail long ago. [28] More recently, there have been a number of attempts to increase the potency of inhibitors of PLP-dependent enzymes that contain a reactive hydrazide. Ejim et al confirmed the formation of a stable adduct to PLP bound to cystathionine b-lyase with a series of hydrazinocarbonylmethylbenzamides, and they were able to improve inhibitor binding affinity by 50-fold with the preparation of small analogue library.…”

Section: Stabilization Of An Azo-quinonoid Intermediatementioning

confidence: 99%

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Inhibition of Mycobacterium tuberculosis Transaminase BioA by Aryl Hydrazines and Hydrazides

et al. 2014

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7,8-diaminopelargonic acid synthase (BioA) of Mycobacterium tuberculosis is a recently validated target for therapeutic intervention in the treatment of tuberculosis (TB). Using biophysical fragment screening and structural characterization of compounds, we have identified a potent aryl hydrazine inhibitor of BioA that reversibly modifies the pyridoxal-5’-phosphate (PLP) cofactor, forming a stable quinonoid. Analogous hydrazides also form covalent adducts that can be observed crystallographically but are incapable of inactivating the enzyme. In the X-ray crystal structures, small molecules induce unexpected conformational remodeling in the substrate binding site. We compare these conformational changes to those induced upon binding of the substrate (7-keto-8-aminopelargonic acid), and characterize the inhibition kinetics and the X-ray crystal structures of BioA with the hydrazine compound and analogs to unveil the mechanism of this reversible covalent modification.

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“…[28] More recently, there have been a number of attempts to increase the potency of inhibitors of PLP-dependent enzymes that contain a reactive hydrazide. Ejim et al .…”

Section: Discussionmentioning

confidence: 99%

Section: Stabilization Of An Azo-quinonoid Intermediatementioning

confidence: 99%

Inhibition of Mycobacterium tuberculosis Transaminase BioA by Aryl Hydrazines and Hydrazides

et al. 2014

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“…However, the (3-hydroxybenzyl)hydrazone of PLP and the tert -butylhydrazone of PLP have absorption maxima at 325 and 297 nm . Acid denaturation of GABA-AT inhibited by (3-hydroxybenzyl)hydrazine results in a spectrum nearly identical to that of the (3-hydroxybenzyl)hydrazone of PLP .…”

Section: Discussionmentioning

confidence: 99%

“…According to a definition for mechanism-based inactivation, a compound that inactivates an enzyme simply by reacting with its cofactor is not a mechanism-based inactivator but an affinity-labeling agent. We recently demonstrated that mechanism-based inactivation cannot account for the time-dependent inhibition of GABA-AT from pig brain by (3-hydroxybenzyl)hydrazine …”

mentioning

confidence: 99%

“…We recently demonstrated that mechanism-based inactivation cannot account for the time-dependent inhibition of GABA-AT from pig brain by (3-hydroxybenzyl)hydrazine. 21 The kinetics of three time-dependent inhibitors of GABA-AT, methylhydrazine, (3-hydroxybenzyl)hydrazine, and 3-hydrazinopropionate, which vary significantly in their structural similarity to the substrate GABA (Chart 1) are described here. Furthermore, since mechanism-based inactivation had been previously ruled out for (3-hydroxybenzyl)hydrazine, 21 reversal kinetics for all three time-dependent inhibitors were evaluated to see if they were consistent with slowbinding inhibition.…”

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confidence: 99%

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Slow-Binding Inhibition of γ-Aminobutyric Acid Aminotransferase by Hydrazine Analogues^,

Lightcap

Silverman

1996

J. Med. Chem.

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(3-Hydroxybenzyl)hydrazine and methylhydrazine have been found to be potent slow-binding inhibitors of the pyridoxal 5-phosphate (PLP)-dependent enzyme gamma-aminobutyric acid aminotransferase (GABA-AT). Both compounds follow mechanism A (Morrison, J.F.; Walsh, C. T. Adv. Enzymol. 1988, 61, 201-301) which does not involve formation of a rapidly reversible enzyme-inhibitor complex before the formation of the final tight complex. The rate constant for formation of the enzyme-inhibitor complex determined from the slow-binding kinetics was 2.08 x 10(3) and 1.98 x 10(4) M-1 min-1 for methylhydrazine and (3-hydroxybenzyl)hydrazine, respectively. The rate constant for dissociation of the enzyme--inhibitor complex determined for the slow-binding kinetics was 4.6 x 10(-3) and 5 x 10(-3) min-1, respectively. The inhibition constants calculated from the slow-binding inhibition kinetics are 2.2 microM for methylhydrazine and 0.3 microM for (3-hydroxybenzyl)hydrazine. Reactivation of the inhibited enzyme was not first order, perhaps due to a side reaction of the hydrazine, but was consistent with the results obtained from the slow-binding kinetics. Inhibition constants were calculated from the level of enzyme activity at equilibrium inhibition. These constants are 2.8 and 0.46 microM for methylhydrazine and (3-hydroxybenzyl)hydrazine, respectively, in good agreement with those calculated from the slow-binding inhibition kinetics. 3-Hydrazinopropionate also behaved as a slow-binding inhibitor. However, the dependence of its kinetics on the concentration of inhibitor could not be described by the slow-binding or slow, tight-binding inhibition models. These kinetics could not be described by the tight-binding character of the inhibition because the addition of the competitive inhibitor propionic acid at 100 times its Ki did not affect the shape of the curve for inhibitor concentration dependence. The slow-binding inhibition appeared to require 2-4 molecules of 3-hydrazinopropionate/enzyme. The reactivation of enzyme inhibited by 3-hydrazinopropionate was first order with a rate constant of 6.9 x 10(-3) min-1. Its equilibrium inhibition constant was calculated to be < 20 nM. However, the inhibition constant calculated was dependent on the concentration of inhibitor because of the unusual character discussed above and may be much lower. Only 1 PLP/enzyme dimer reacted with methylhydrazine or (3-hydroxybenzyl)hydrazine, as indicated by Scatchard plots, or with 3-hydrazinopropionate, as shown by a spectrophotometric titration. Slow-binding inhibition does not appear to be the result of a significant enzyme conformational change because there is no change in the tryptophan fluorescence of GABA-AT upon binding either methylhydrazine or 3-hydrazinopropionate. Implications for the design of hydrazine inhibitors of GABA-AT are discussed.

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Phenylethylidenehydrazine, a novel GABA-transaminase inhibitor, reduces epileptiform activity in rat hippocampal slices

Duffy¹,

Nguyen²,

Baker³

2004

Neuroscience

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Time-dependent inhibition of γ-aminobutyric acid aminotransferase, by 3-hydroxybenzylhydrazine

Cited by 4 publications

References 12 publications

Inhibition of Mycobacterium tuberculosis Transaminase BioA by Aryl Hydrazines and Hydrazides

Inhibition of Mycobacterium tuberculosis Transaminase BioA by Aryl Hydrazines and Hydrazides

Slow-Binding Inhibition of γ-Aminobutyric Acid Aminotransferase by Hydrazine Analogues^,

Phenylethylidenehydrazine, a novel GABA-transaminase inhibitor, reduces epileptiform activity in rat hippocampal slices

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Time-dependent inhibition of γ-aminobutyric acid aminotransferase, by 3-hydroxybenzylhydrazine

Cited by 4 publications

References 12 publications

Inhibition of Mycobacterium tuberculosis Transaminase BioA by Aryl Hydrazines and Hydrazides

Inhibition of Mycobacterium tuberculosis Transaminase BioA by Aryl Hydrazines and Hydrazides

Slow-Binding Inhibition of γ-Aminobutyric Acid Aminotransferase by Hydrazine Analogues,

Phenylethylidenehydrazine, a novel GABA-transaminase inhibitor, reduces epileptiform activity in rat hippocampal slices

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Slow-Binding Inhibition of γ-Aminobutyric Acid Aminotransferase by Hydrazine Analogues^,