Merocyanine 540-sensitized photoinactivation of soluble and membrane-bound enzymes in L1210 leukemia cells.

Merocyanine 540 (MC 540) is a photosensitizing dye that is used clinically for the purging of autologous bone marrow grafts and preclinically for the inactivation of enveloped viruses in blood products. Its mechanism of action is not yet well understood. This paper investigates the sites of MC 540-mediated photodamages in L1210 leukemia cells by examining the effects of MC 540-sensitized photoirradiation on several soluble and membrane-bound marker enzymes. When exposed to MC 540 and white light under a standard set of conditions, the activities of Na+/K(+)-ATPase, Mg2(+)-ATPase, and 5'-nucleotidase (three plasma membrane-bound enzymes) were reduced by 54, 49, and 55%, respectively. None of the intracellular enzymes included in this survey was affected by MC 540-sensitized photoirradiation as long as the plasma membrane remained intact. The two soluble enzymes, lactate dehydrogenase and malate dehydrogenase, remained refractory to MC 540-sensitized photoirradiation even after the plasma membrane had been disrupted. By contrast, the activities of the membrane-bound enzymes, NADPH-cytochrome c reductase and succinate dehydrogenase, were reduced in cell lysates by 55 and 81%, respectively. Purified NADPH-cytochrome c reductase was about 3 times less sensitive than the microsomal enzyme, suggesting that the membrane environment facilitated photoinactivation. The MC 540-sensitized photoinactivation of enzymes was accelerated in the presence of deuterium oxide and inhibited if oxygen in the medium was displaced by nitrogen or azide was added to the medium. Taken together, these data support the view that the plasma membrane is a major target of MC 540-mediated photodamages, that the inactivation of membrane-bound enzymes is an oxidative process, and that at least some photodynamic damages are mediated by type II chemistry.

Target inactivation analysis applied to determination of molecular weights of rat liver proteins in the purified state and in microsomal membranes.

In principle, target inactivation analysis provides a means of determining the molecular weights (Mr) and states of aggregation of proteins in native environments where they are functionally active. We applied this irradiation technique to the rat liver microsomal membrane proteins: cytochrome b5, epoxide hydrolase, flavin-containing monooxygenase, NADH-ferricyanide reductase, NADPH-cytochrome P-450 reductase, and seven different forms of cytochrome P-450. Catalytic activities, spectral analysis of prosthetic groups, and sodium dodecyl sulfate-polyacrylamide electrophoresis/peroxidase-coupled immunoblotting were used to estimate apparent Mr values in rat liver microsomal membranes. Except in one case (cytochrome P-450PCN-E), the estimated Mr corresponded most closely to that of a monomer. Purified cytochrome P-450PB-B, NADPH-cytochrome P-450 reductase and epoxide hydrolase were also subjected to target inactivation analysis, and the results also suggested monomeric structures for all three proteins under these conditions. However, previous hydrodynamic and gel-exclusion results clearly indicate that all three of these proteins are oligomeric under these conditions. The discrepancy between target inactivation Mr estimates and hydrodynamic results is attributed to a lack of energy transfer between monomeric units. Thus, while P-450PCN-E may be oligomeric in microsomal membranes, target inactivation analysis does not appear to give conclusive results regarding the states of aggregation of these microsomal proteins.

Influence of gamma-rays on the mouse liver cytochrome P450 system and its modulation by phenothiazine drugs.

PURPOSE: Phenothiazine drugs have been found to sensitize hypoxic cancer cells while offering protection to normal cells. Since phenothiazines are known to induce the cytochrome P450 system, its radiomodulation by phenothiazines has been examined. MATERIALS AND METHODS: Mice were administered phenothiazines intraperitoneally and irradiated with different doses of gamma-rays at 1.38 Gy/min. The activities of NADPH-cytochrome P450 reductase and NADH-cytochrome b5 reductase, the content of cytochrome P450 and b5, the extent of lipid peroxidation as well as the activities of LDH, XO, SOD, GST and DTD were determined in the liver. RESULTS: The levels of different components of the cytochrome P450 system and antioxidant enzymes were enhanced up to 5 Gy and decreased thereafter. However, a progressive increase was noticed in peroxidative damage and the activities of LDH and XO. Administration of phenothiazines enhanced the radiation effect on components of the cytochrome P450 system (except NADH-cytochrome b5 reductase) and the activities of SOD, GST and DTD. Concomitantly, phenothiazines inhibited lipid peroxidation, LDH and XO. CONCLUSIONS: Activation of the cytochrome P450 system by phenothiazines leading to the enhancement of antioxidant potential of animals and free-radical scavenging are attributes of the radioprotective action of phenothiazines.

Blue light mediated photoreduction of the flavoprotein NADPH-cytochrome P450 reductase. A Förster-type energy transfer.

The absorption spectra and the corresponding molar absorption coefficients of the fluorophores umbelliferone, FAD and FMN and of the FAD and FMN containing flavoprotein NADPH-cytochrome P450 reductase of different oxydation-reduction states are documented. Binding spectra of the ligand umbelliferone with the CYP2B1:NADPH-cytochrome P450 reductase-complex were determined by difference spectroscopy. The Scatchard plot of the equilibrium ligand binding shows a high affinity part and a low affinity part of 12 and 34 umbelliferone binding sites per CYP2B1:reductase-complex molecule, respectively. The fluorescence excitation and emission spectra of the donor molecule umbelliferone and the acceptor molecules FAD and FMN are given. The fluorescence spectra of the reaction components under test conditions of CYP2B1-dependent 7-ethoxycoumarin-O-deethylase are measured. The excitation energy transfer from the donor umbelliferone (lambda E = 380 nm; lambda F = 460 nm) to the acceptor molecule FMN (lambda E = 465 nm; lambda F = 525 nm) was examined under assay conditions. The results demonstrate that a radiationless Förster-type energy transfer takes place in the presence of the CYP2B1:reductase-complex. It turned out that this effect is a function of the protein complex-concentration. The data presented here combined with previously made observations by Müller-Enoch (Müller-Enoch D. (1994), Z. Naturforsch. 49c, 763-771) support the finding that the umbelliferone molecules, n = 12-34, bound per mole of CYP2B1:reductase-complex, transfer their absorbed light energy radiationless to the FAD binding domain. The complex formed containing 12 or 34 molecules of umbelliferone provides absorption coefficient values at lambda = 380 nm of 78 and 221 mM-1.cm-1, respectively. The Förster-type energy transfer from the donor umbelliferone to the acceptor FAD not only leads to a light activation of the singlet state of FAD but also to a conformational change of the amino acids close to the FAD binding side to favour the encaging of the FAD* triplet state which reacts with the NADPH to form the FADH2 reductase. Due to this process the overall reaction can start with the unquenched excited FAD* triplet state as an intermediate which is about 30 kJ/mol lower in energy than the dark reaction.

Measure of enzymatic activity coincident with 2450 MHz microwave exposure.

Enzyme preparations were exposed to microwave radiation at 2450 MHz and enzymatic activity was simultaneously monitored spectrophotometrically with a crossed-beam exposure detection system. Enzymes studied were glucose 6-phosphate dehydrogenase from human red blood cells and yeast, adenylate kinase from rat liver mitochondria and rabbit muscle, and rat liver microsomal NADPH cytochrome c reductase. No difference was found between the specific activity at 25 degrees C of unirradiated controls and enzyme preparations irradiated at an absorbed dose rate of 42 W/kg.

EM-field effect upon properties of NADPH-cytochrome P-450 reductase with model substrates.

Artificial substrates, including ferricyanide and dichlorophenol indophenol (IP), are frequently used to model the activity of NADPH-cytochrome P-450 reductase, in the xenobiotic-metabolic pathway catalyzed by the P-450 complex. Here, the two oxidants were compared in a microsomal preparation from chicken liver. Low-energy 9.14 GHz perturbation affected both reactions similarly, though the IP reaction may be more sensitive to extremely low energy levels. The reactions of the two oxidants differed from each other in their response to the prior incubation of the microsomes with carbon monoxide and to the presence of superoxide dismutase. The mechanics of the reduction of ferricyanide and the reduction of IP are not identical and the electron-flow paths may be dissimilar. Microwave effect cannot be attributed a temperature change in the reaction medium; it appears to occur at the level of the electron-flow path across the dual-flavin reductase.

Reconstitution studies on the involvement of radiation-induced lipid peroxidation in damage to membrane enzymes.

The effect of radiation on the drug-metabolizing enzyme system of microsomes, reconstituted with liposomes of microsomal phospholipids, NADPH-cytochrome P-450 reductase and cytochrome P-450, was examined to elucidate the role of lipid peroxidation of membranes in radiation-induced damage to membrane-bound enzymes. The reconstituted system of non-irradiated enzymes with irradiated liposomes showed a low activity of hexobarbital hydroxylation, whereas irradiated enzymes combined with non-irradiated liposomes exhibited an activity equal to that of unirradiated controls. Irradiation of liposomes caused a decrease in cytochrome P-450 content by destruction of the haem of cytochrome P-450 and also inhibited the binding capacity of cytochrome P-450 for hexobarbital. The relationship between radiation-induced lipid peroxidation and membrane-bound enzymes is discussed.

[Effect of radioprotectors on lipid peroxidation in liver microsomes induced by ultraviolet irradiation of the skin in rats]. / Vliianie radioprotektorov na perekislenie lipidov mikrosom pecheni, indutsirovannoe ul'trafioletovym oblucheniem kozhi krys.

The modifying effect of radioprotectors (serotonin, cysteamine, ionol) on lipid peroxidation intensification of liver microsomes caused by rat skin ultraviolet radiation has been studied. A possible mechanism of action of these compounds on the investigated indexes during their preventive injection is under discussion.