Related Experiment Video
Updated: Sep 13, 2026

Bio-layer Interferometry for Measuring Kinetics of Protein-protein Interactions and Allosteric Ligand Effects
Published on: February 18, 2014
Molecular interactions in intermediate and transition states in the self-stimulated inhibition of enzymes
H U Demuth1, J Heins, H Fujihara
1Department of Drug Biochemistry, Martin Luther University, Halle-Wittenberg, GDR.
Abstract:
Di-isopropyl fluorophosphate (DFP) and other organophosphorus inhibitors recruit the catalytic power of their target enzymes: the enzyme catalyzes its own irreversible phosphorylation. The magnitude of the catalytic acceleration can approach the factor by which the enzyme catalyzes its own acylation by natural substrates. The reaction of DFP with five serine proteases [chymotrypsin, elastase, dipeptidyl peptidase IV (DP IV), subtilisin and thermitase] exhibits in all cases the same pH dependence as does enzyme acylation by natural substrates. Chymotrypsin and elastase form a "fast" class of enzymes which react about ten-fold faster than the other three "slow" enzymes. All enzymes show k(HOH)/k(DOD) of about 2 but the proton inventory indicates one-proton character for "slow" enzymes and multiproton character for "fast" enzymes. Enthalpies of activation are about 33 kJ/mol (subtilisin, "slow") and 10 kJ/mol (elastase, "fast"). Entropies of activation are about -120 J.T-1.mol-1 (subtilisin, "slow") and -175J.T-1.s-1 (elastase, "fast"; T = temperature in K).
Related Concept Videos
Induced-fit Model
Enzymes exhibit substrate specificity, meaning that they can only bind to certain substrates. This is mainly determined by the shape and chemical characteristics of...
Feedback Inhibition
Enzyme Inhibition
Enzymes
Enzyme deficiencies can often translate into life-threatening diseases. For example, a genetic abnormality resulting in the deficiency of the enzyme G6PD...
Introduction to Mechanisms of Enzyme Catalysis
Introduction to Mechanisms of Enzyme Catalysis

