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Enzyme Inhibition

Enzyme Inhibition

Inhibitors are molecules that reduce enzyme activity by binding to the enzyme. In a normally functioning cell, enzymes are regulated by a variety of inhibitors. Drugs and other toxins can also inhibit enzymes. Some inhibitors bind to the enzyme’s active site, while others inhibit enzymatic activity by binding to other sites on the protein structure.

Enzymes

Enzymes

Inside living organisms, enzymes act as catalysts for many biochemical reactions involved in cellular metabolism. The role of enzymes is to reduce the activation energies of biochemical reactions by forming complexes with its substrates. The lowering of activation energies favor an increase in the rates of biochemical reactions.
Enzyme deficiencies can often translate into life-threatening diseases. For example, a genetic abnormality resulting in the deficiency of the enzyme G6PD...

Ligand Binding and Linkage

Ligand Binding and Linkage

Allosteric proteins have more than one ligand binding site; the binding of a ligand to any of these sites influences the binding of ligands to the other sites. When a protein is allosteric, its binding sites are called coupled or linked. In the case of enzymes, the site that binds to the substrate is known as the active site and the other site is known as the regulatory site. When a ligand binds to the regulatory site, this leads to conformational changes in the protein that can influence the...

ATP Synthase: Mechanism

ATP Synthase: Mechanism

In animals, the mitochondrial F1F0 ATP synthase is the key protein that synthesizes ATP molecules through a complex catalytic mechanism. While the nuclear genome encodes the majority of ATP synthase subunits, the mitochondrial genome encodes some of the enzyme's most critical components. The formation of this multi-subunit enzyme is a complex multi-step process regulated at the level of transcription, translation, and assembly. Defects in one or more of these steps can result in decreased ATP...

ATP Synthase: Structure

ATP Synthase: Structure

ATP synthase or ATPase is among the most conserved proteins found in bacteria, mammals, and plants. This enzyme can catalyze a forward reaction in response to the electrochemical gradient, producing ATP from ADP and inorganic phosphate. ATP synthase can also work in a reverse direction by hydrolyzing ATP and generating an electrochemical gradient. Different forms of ATP synthases have evolved special features to meet the specific demands of the cell. Based on their specific feature, ATP...

Allosteric Proteins-ATCase

Allosteric Proteins-ATCase

Binding sites linkages can regulate a protein's function. For example, enzyme activity is often regulated through a feedback mechanism where the end product of the biochemical process serves as an inhibitor.
Aspartate transcarbamoylase (ATCase) is a cytosolic enzyme that catalyzes the condensation of L-aspartate and carbamoyl phosphate to N-carbamoyl-L-aspartate. This reaction is the first step in pyrimidine biosynthesis. UTP and CTP, the end products of the pyrimidine synthesis pathway,...

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Related Experiment Video

Updated: Jul 12, 2026

Direct Detection of the Acetate-forming Activity of the Enzyme Acetate Kinase

Direct Detection of the Acetate-forming Activity of the Enzyme Acetate Kinase

Published on: December 19, 2011

Structural analyses of a malate dehydrogenase with a variable active site.

J K Bell¹, H P Yennawar, S K Wright

¹Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis 55455, USA.

The Journal of Biological Chemistry

|June 5, 2001

Summary

Malate dehydrogenase

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Last Updated: Jul 12, 2026

Direct Detection of the Acetate-forming Activity of the Enzyme Acetate Kinase

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Published on: December 19, 2011

Expression, Purification, Crystallization, and Enzyme Assays of Fumarylacetoacetate Hydrolase Domain-Containing Proteins

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Published on: June 20, 2019

Modeling an Enzyme Active Site using Molecular Visualization Freeware

Modeling an Enzyme Active Site using Molecular Visualization Freeware

Published on: December 25, 2021

Area of Science:

Biochemistry
Enzymology
Structural Biology

Background:

Malate dehydrogenase catalyzes malate oxidation to oxaloacetate.
Enzyme specificity is conferred by active site arginines coordinating substrate carboxyl groups.

Purpose of the Study:

Investigate the role of Arg-153 in malate dehydrogenase substrate specificity using the R153C mutant.
Determine the structural basis for altered enzyme activity in the R153C mutant.

Main Methods:

X-ray crystallography of the NAD binary complex.
Analysis of NAD-pyruvate ternary complex.
Energy-minimized molecular modeling of R153C analogues.

Main Results:

The R153C mutation shifts a bound sulfate ion in the active site, suggesting substrate misalignment.
Pyruvate binds via backbone interactions, not arginine coordination, in the R153C mutant.
Molecular models indicate potential favorable interactions for modified side chains, but native activity is not restored.

Conclusions:

Precise positioning of the Arg-153 guanidino side chain is critical for optimal substrate orientation and high enzymatic activity.
The R153C mutation leads to reduced catalytic turnover due to altered substrate binding and positioning.