Chemical modification of the histidine residues of purified hepatic cytochrome p-450: Influence on substrate binding and the haemoprotein spin state

Gibson, Gordon; Tamburini, Paul P.

doi:10.1016/s0009-2797(86)80097-7

Cited by 9 publications

(2 citation statements)

References 31 publications

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“…min −" , respectively, were obtained for untreated haemoprotein and pigment containing 10.3 N-carbethoxyhistidine groups per mol of enzyme. This finding is at variance with a previous report, indicating that exhaustive carbethoxylation of phenobarbital-inducible rat liver microsomal cytochrome P-450, sharing 77 % structural identity with P-450 2B4 [36], results in hampered binding of benzphetamine [37], another type I compound.…”

Section: Characteristics Of P-450 2b4 Modification By Depccontrasting

confidence: 99%

Histidine residues in rabbit liver microsomal cytochrome P-450 2B4 control electron transfer from NADPH-cytochrome P-450 reductase and cytochrome b5

Hlavica¹,

Lehnerer²,

Eulitz³

1996

Biochemical Journal

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Treatment of cytochrome P-450 2B4 (P-450 2B4) with diethylpyrocarbonate to introduce 10-11 equivalents of acylating agent per polypeptide chain resulted in the selective derivatization of histidine residues characterized by differential susceptibility toward the modifier. Second-derivative spectral analysis as well as fluorescence measurements disproved gross alterations in P-450 2B4 structure as a consequence of labelling. The modified haemoprotein retained its ability to bind hexobarbital and catalyse cumene hydroperoxide-sustained N-demethylation of the barbiturate. However, there was a steady attenuation of NAD(P)H-driven electron flux with increasing extent of P-450 2B4 carbethoxylation in reconstituted systems fortified with either NADPH-cytochrome P-450 reductase or NADH-cytochrome b5 reductase/cytochrome b5 as the redox partners, with 50% inhibition occurring when 6-7 histidines were blocked. Hampered P-450 2B4 reductase activities recovered to differing degrees upon treatment of the acylated mono-oxygenase with neutral hydroxylamine. Spectral data indicated that docking of the redox components to derivatized P-450 2B4 was not perturbed, so that disruption of the electron flows most likely resulted from some injury of the electron-transfer mechanisms.

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Section: Characteristics Of P-450 2b4 Modification By Depccontrasting

confidence: 99%

Histidine residues in rabbit liver microsomal cytochrome P-450 2B4 control electron transfer from NADPH-cytochrome P-450 reductase and cytochrome b5

Hlavica¹,

Lehnerer²,

Eulitz³

1996

Biochemical Journal

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“…On the other hand, base catalysis due to specific amino acid residues close to the distal heme ligand of the diverse P-450s could be hypothesized to be involved. Indeed, histidine has been recognized to play some role in the P-450-dependent conversion of N,N-dimethylaniline to the N-oxide (66), and this amino acid is also critical in the interaction of benzphetamine with highly purified phenobarbital-inducible P-450 (67). Binding of N-alkylamines to the activesite base thus could interrupt a proton shuttle from the a-carbon, favoring oxygen rebound to the aminium radical.…”

Section: Oxygenation Of Secondary Andmentioning

confidence: 99%

Some aspects of the role of cytochrome P‐450 isozymes in the n‐oxidative transformation of secondary and tertiary amine compounds

Hlavica¹,

Lehnerer²

1995

J. Biochem. Toxicol.

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Indirect evidence of the participation of cytochrome P-450 (P-450) in the microsomal N-oxygenation of secondary and tertiary nitrogen functions is presented by studies employing diagnostic modifiers of the hemoprotein system as well as antibodies directed toward the diverse P-450 isoforms and NADPHcytochrome P-450 reductase. Experiments with recombinant hemoproteins or P-450 isozymes directly purified from the tissues of various animal species support the results obtained by the inhibitor assays. Although the intermediacy of aminium radicals is thought to be restrictive to P-450-catalyzed N-oxygenation of secondary and tertiary amine groups bearing accessible hydrogens on the a-carbon, numerous exceptions to this rule are documented. It is proposed that aminium radicals partition between oxygen rebound and a-hydrogen abstraction to yield a finite level of N-oxygenated product in all P-450-mediated amine oxidations, the partition ratio depending on the amine structure and particular P-450 isozyme operative. In some instances, N-oxygenation appears to proceed by peroxidatic mechanisms. The relative contribution of P-450 to the N-oxygenation of secondary and tertiary amines in crude preparations or live animals, where competition with the flavin-containing monooxygenase (FMO) OCcurs, seems to be a function of the relative amounts and catalytic capacities of the two enzyme systems. Both parameters are species and tissue dependent. Accordingly, the extent to which P-450 contributes to total N-oxidative turnover of the amine substrates varies from minor to major.

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Chemical Probes of Cytochrome P450 Structure

Bernhardt¹

1993

Cytochrome P450

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Chemical modification of the histidine residues of purified hepatic cytochrome p-450: Influence on substrate binding and the haemoprotein spin state

Cited by 9 publications

References 31 publications

Histidine residues in rabbit liver microsomal cytochrome P-450 2B4 control electron transfer from NADPH-cytochrome P-450 reductase and cytochrome b5

Histidine residues in rabbit liver microsomal cytochrome P-450 2B4 control electron transfer from NADPH-cytochrome P-450 reductase and cytochrome b5

Some aspects of the role of cytochrome P‐450 isozymes in the n‐oxidative transformation of secondary and tertiary amine compounds

Chemical Probes of Cytochrome P450 Structure

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