title: The activation of the cytochrome P-450 dependent monooxygenase system by light.
abstract: The cytochrome P-450 dependent monooxygenase system of rat liver microsomes is investigated by light dosimetry (action spectroscopy). The scoparone-O-demethylation activity is enhanced by light and depends on the wavelength of the irradiating light. The relative increase of the activity (about 15%) by the irradiating light (approximately 0.5 mW/cm2) is maximal at a wavelength of 400 nm. The light induced enhancement of the 7-ethoxycoumarin-O-deethylase activity was measured in reconstituted systems, consisting of one of two P-450 enzymes (P-450 beta NF-B and P-450 PB-B) with the NADPH-cytochrome P-450 reductase. The action spectrum of the reconstituted P-450 beta NF-B:NADPH-P-450 reductase complex shows a maximum between 420 and 440 nm. The relative increase of the activity induced by light of 420 nm was 7.3% and 9% for the reconstituted systems of P-450 beta NF-B and P-450 PB-B, respectively. The results are discussed in analogy to the classic experiments of Warburg with its blocked CO-enzyme-complex. The results can best be explained by the assumption that the light induced enhancement of the enzyme activity is due to an excitement of those intermediate states of the P-450 catalytic cycle (ferric and ferrous state of the heme iron) which are rate limiting.
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism; D004789:Enzyme Activation; D007700:Kinetics; D008027:Light; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D009251:NADPH-Ferrihemoprotein Reductase / Q000302:isolation & purification / Q000378:metabolism; D010105:Oxygenases / Q000378:metabolism* / Q000528:radiation effects; D051381:Rats; D011919:Rats, Inbred Strains
chemical_list: D003577:Cytochrome P-450 Enzyme System; D010105:Oxygenases; D009251:NADPH-Ferrihemoprotein Reductase