ABSTRACT
We studied in vitro effects of four 1,2,3,4-tetrahydroimidazo[4,5-c]-pyridine derivatives formed in the reaction of the corresponding aldehydes with histidine on the rate of ethanol oxidation by alcohol dehydrogenase isoforms from human liver. None of test compounds inhibited ethanol oxidation by these enzymes. Some of them increased alcohol dehydrogenase activity to 220-240% of the initial level. Only one test compound accelerated ethanol oxidation by b1b2-alcohol dehydrogenase (150% of the control). The molecular mechanism underlying these effects of 1,2,3,4-tetrahydroimidazo[4,5-c]-pyridine derivatives on ethanol oxidation by alcohol dehydrogenase isoforms from human liver is discussed.
Subject(s)
Alcohol Dehydrogenase/metabolism , Ethanol/metabolism , Liver/enzymology , Pyridines/pharmacology , Enzyme Activation , Humans , In Vitro Techniques , Isoenzymes/metabolism , Oxidation-Reduction/drug effects , Substrate Specificity/drug effectsABSTRACT
Functional groups essential for high- and low-affinity [3H]imipramine (IMI) binding were determined by the method of chemical modification. The high-affinity recognition sites contained cysteine and lysine amino acid residues, but not aspartic or glutamic acid residues. The low-affinity recognition sites contained only cysteine residues. Moreover, probably only part of these sites contained these residues. The arginine, tyrosine and histidine residues are not likely to be functionally important for the [3H]IMI binding process. Analysis of the structure-function interaction of drug molecules reveals that, for all substances with high displacement ability, there is a conformation in which they can react with high-affinity IMI recognition sites. Data obtained allowed us to construct a tentative structure model of the high-affinity recognition IMI binding site.
Subject(s)
Blood Platelets/chemistry , Carrier Proteins , Cell Membrane/chemistry , Receptors, Drug , Receptors, Neurotransmitter/chemistry , Amino Acids/analysis , Amino Acids/chemistry , Antidepressive Agents, Tricyclic/pharmacology , Blood Platelets/metabolism , Cell Membrane/metabolism , Cerebral Cortex/drug effects , Cerebral Cortex/metabolism , Humans , Hydrogen-Ion Concentration , In Vitro Techniques , Kinetics , Models, Structural , Psychotropic Drugs/pharmacology , Receptors, Neurotransmitter/metabolism , Structure-Activity Relationship , Sulfhydryl Compounds/chemistry , Sulfhydryl Reagents/pharmacologyABSTRACT
We have confirmed the presence of two different classes of [3H]imipramine ([3H]IMI) binding sites on human platelets: high-affinity (Kd = 0.52 nM, Bmax = 1670 fmol/mg protein) and low-affinity (Kd = 101 nM, Bmax = 8,000 fmol/mg protein) binding sites. The high-affinity component of [3H]IMI binding can also be obtained separately as the difference between specific [3H]IMI binding in Na-containing and Li-containing incubation buffer. The low-affinity component can be obtained as the difference between [3H]IMI binding in 50 mM Tris-HCl, 5 mM KCl, 120 mM LiCl, (pH 7.5) in the absence and presence of 0.1 mM IMI. The chemical modification of SH groups was performed with Ellman's reagent (10 mM, 40 min at 23 degrees C). The high-affinity component of the binding was totally inhibited while the low-affinity component only decreased by 39%. No decrease in [3H]IMI specific binding was observed when the modification of SH groups was carried out in the presence of 1 microM IMI. The inhibition of high- and low-affinity [3H]IMI binding was reversible since it was completely restored by incubation of modified membranes with 1,4-dithioerythritol (DTE). The reduction of SS groups by DTE (10 mM, 1 h at 23 degrees C) in the intact membrane preparation produced an increase in total number of binding sites of the high-affinity component of [3H]IMI binding by 50%.
