title: Effects of detergent on substrate binding and spin state of purified liver microsomal cytochrome P-450LM2 from phenobarbital-treated rabbits.
abstract: Spectral changes accompanying the binding of the nonionic detergent n-octyl beta-D-glucopyranoside (n-octyl glucoside) to cytochrome P-450LM2 purified from liver microsomes of phenobarbital-treated rabbits have been compared to changes in catalytic activity obtained in a reconstituted system consisting of various levels of detergent, P-450LM2, and NADPH-cytochrome P-450 reductase. In the absence of substrate and reductase, addition of n-octyl glucoside to 2-3 mM resulted in a difference spectrum (detergent-bound minus detergent-free cytochrome) characterized by a small maximum at 390 nm and a minimum at 410 nm, suggestive of a slight stabilization of the high-spin (S = 5/2) state of the cytochrome. As the detergent concentration was increased to 4-8 mM (corresponding to maximal activity and pentameric or hexameric P-450), a new peak appeared at 427 nm while the minimum remained at 410 nm. Between 10 and 30 mM n-octyl glucoside (conditions which produced catalytically inactive and monomeric P-450) the minimum in the difference spectrum shifted to 390 nm and the maximum to 425 nm, characteristic of a shift in spin equilibrium toward low-spin (S = 1/2) cytochrome. At low and high detergent concentrations, substrate [d-benzphetamine with n-octyl glucoside or cyclohexane with the zwitterionic detergent 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS)] was bound to P-450LM2 with formation of high-spin P-450, although the increase in high-spin cytochrome was less at high detergent levels than at low. The affinity of P-450 for substrate decreased by 2-3-fold at high detergent.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism*; D003902:Detergents / Q000494:pharmacology*; D005960:Glucosides / Q000494:pharmacology*; D006027:Glycosides / Q000494:pharmacology*; D007700:Kinetics; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D010634:Phenobarbital / Q000494:pharmacology*; D011485:Protein Binding; D011817:Rabbits; D013053:Spectrophotometry; D013501:Surface-Active Agents / Q000494:pharmacology*
chemical_list: D003902:Detergents; D005960:Glucosides; D006027:Glycosides; D013501:Surface-Active Agents; C018619:octyl-beta-D-glucoside; D003577:Cytochrome P-450 Enzyme System; D010634:Phenobarbital