Search PubMed⌕ Search

Biomedical subjects

M H Bickel

Publications and source records attributed to M H Bickel.

At least 55 records · Page 3Linked to original sources
PubMed1979

A method to estimate binding constants at variable protein concentrations.

The association constants of the binding of chlorpromazine and imipramine to serum albumin at low saturation of the protein were determined by a new experimental approach with the protein concentration rather than the ligand concentration being varied. This approach is suitable for estimating binding constants in systems with one class of binding sites. In addition, the method is proposed to complement conventional binding studies of systems with two classes of binding constant with higher accuracy.

Chlorpromazine↗
PubMed1979

Interference of UDP-glucuronyltransferase and beta-glucuronidase activity in rat liver microsomes at pH 7.5 with p-nitrophenol and p-nitrophenylglucuronide as substrates.

Microsomal fraction contains the whole of hepatic UDP-glucuronyltransferase as well as part of beta-glucuronidase. The activities of the two enzymes were assayed under identical conditions using untreated male rat liver microsomes at pH 7.5. In a 30-min incubation with p-nitrophenol and UPD-glucuronic acid, a net glucuronide formation of 0.010 mumol.min-1.g.liver-1 was measured. In the presence of saccharolactone at concentrations selectively blocking beta-glucuronidase, the glucuronidation rate was 0.015 mumol.min-1.g.liver-1. Using the kinetic parameters of beta-glucuronidase (Km = 0.06 mmol/l p-nitrophenylglucuronide, Vm = 0.075 mumol pNP formed.h-1.g.liver-1) determined in the absence of UDP-glucuronic acid, to correct for the beta-glucuronidase's interference on the glucuronidation process, a glucuronide formation of 0.011 mumol.min-1.g.liver-1 was calculated.

Animals↗
PubMed1978

Interaction of chlorpromazine with organic solvents and fatty acids as studied by UV-spectrophotometry.

The magnitude of the UV-spectral change of chlorpromazine increases in the presence of increasing concentrations of alcohols or fatty acids and with increasing chain length. A maximum is reached with 14.0- or 16.0-fatty acids. The differential spectrum is still larger with unsaturated fatty acids, a maximum effect being obtained with one cis-double bond. The spectral change is abolished by chaotropic and enhanced by antichaotropic agents.

Alcohols↗
PubMed1977

Membrane lipids as intracellular binders of chlorpromazine and related drugs.

Equilibrium dialysis studies with chlorpromazine (CPZ) showed affinity and binding capacity values which were not significantly different with the following binders: rat liver microsomes, mitochondria, mitochondrial membranes, brain synaptosomes, myelin vesicles, and red blood cell membranes. There was no binding to cytosol or mitochondrial matrix. The same binding values as above were obtained with protein-free liposomes of lipids extracted from microsomes, mitochondrial and red cell membranes and of pure egg lecithin. The binding values of the two classes of binding sites of all these preparations were K1=2.7+/-1.0-10(4) M-1, K2=3.8+/-1.7-10(3) M-1, C1=580+/-+/-230 and C1+2=1410+/-500 nmole/mg phospholipid. These values were not altered by elimination of the polar head groups of phospholipids with phospholipase C. The results were confirmed by a UV spectroscopic method whereby the strongest binding signals were obtained with CPZ in the presence of fatty acids such as oleate. It is concluded that the major intracellular binders of CPZ and related drugs are the nonpolar moieties of membrane phospholipids, whereby hydrophobic interactions are mainly involved.

Animals↗
PubMed1976

Characterization of interactions of phenothiazines and related drugs with lipids by UV-spectrophotometry.

The UV-spectrum of chlorpromazine undergoes a red shift in the presence of vesicles of biological membranes or phospholipids, triglycerides, serum lipoproteins or fatty acids. The resulting difference spectrum has two positive peaks at about 260 and 320 nm and two negative peaks at 250 and 290 nm. This interaction signal, which was elicited in the presence of as little as 3 muM oleic acid, was dependent on the concentrations of both ligand and binder. It was abolished by 8 M urea, diminished by temperature increase up to 70 degrees C, but not changed by varying the ionic strength from 0 to 0.5. The chlorpromazine-triglyceride interaction signal was strongly enhanced with pH increasing from 6 to 10. The signal was only obtained with ligands fulfilling specific structural requirements, e.g., phenothiazines and most iminostilbenes, but not carbamazepine, imipramine, and amitriptyline.

Animals↗
PubMed1975

Binding of chlorpromazine and imipramine to red cells, albumin, lipoproteins and other blood components.

The binding of model drugs to human blood and individual blood components has been determined by equilibrium dialysis and expressed in terms of classes of binding sites, association constants and binding capacities. Chlorpromazine and imipramine are bound to three major components: membranes of red cells, albumin, and lipoproteins. The affinity and capacity of lipoprotein binding is at least as high as that of albumin and is equally distributed on HDL, LDL, VLDL, and on the chylomicrons. White blood cells and platelets are of minor importance in terms of binding capacity. No binding was detected with gamma-globulins or alpha- or beta-globulins other than lipoproteins. In contrast, salicylic acid was not bound to red cells or lipoproteins.

Binding Sites↗
PubMed1975

Liver microsomal beta-glucuronidase and UDP-glucuronyltransferase.

Both UDP-glucuronyltransferase (GT) and beta-glucuronidase (betaG) were assayed in untreated liver microsomes. Optimum assay conditions were established with rat liver microsomes using p-nitrophenol (pNP) and its glucuronide (pNPGA) at the pH optima of GT (7.5) and betaG (4.5). The activities of the two enzymes were compared using microsomes from rats, mice, pigs, cattle and horses, with pNP, pNPGA, and phenolphthalein as substrate, in the presence of various cofactors and inhibitors at pH 7.5 and 4.5. These data disclose pronounced differences with respect to species, substrate and other experimental conditions, thereby precluding the establishment of general optimum conditions. The two enzymes were also assayed under strictly identical conditions using pNP and pNPGA and rat liver microsomes at pH 7.5 in the presence and absence of UDP-glucuronate disodium (UDPGA), activators (ATP;UDP-N-acetylglucosamine) and inhibitors. When provided with a functional level of UDPGA, both enzymes proved active under those conditions, and a conjugation-deconjugation interplay was indicated. The two processes could be selectively and totally inhibited by Zn2+ and saccharolactone. The results suggest that conjugation-deconjugation-reconjugation cycles may be operative in the metabolism of drugs in vivo, taking place already at the level of the liver endoplasmic reticulum.

Adenosine Triphosphate↗