Essential Role of His163 of Cytochrome P450 1A2 in Catalytic Functions Associated with Cytochrome b5

Mayuzumi, Hiroshi; Shimizu, Tôru; Sambongi, Chiaki; Hiroya, Kou; Hatano, Masahiro

doi:10.1006/abbi.1994.1180

Cited by 26 publications

(5 citation statements)

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“…Similarly, excess 1-butanol converted rat CYP1A2 to predominantly low-spin hemoprotein characterized by an E 0' value of 297 mV, which is close to 304 mV found for the mixed-spin congener [13] ( Table 2). These findings would disprove spin state to be essential in steering the enzyme's electrochemical behaviour, which is likely to be maintained by some interaction of residue H163 with the heme prosthetic group [117]. Moreover, rabbit CYP1A2 has been demonstrated to be 84% low-spin in the absence of substrate and 87% high-spin in the presence of 7,8-benzoflavone; nevertheless, NADPH-driven rates of reduction of the two spin components, when reconstituted with OR, were almost identical, casting doubt on spin-state control over the electron fluxes in these systems [25].…”

Section: Studies With Highly Purified and Recombinant P450 Systems Thmentioning

confidence: 82%

“…In this respect, a series of determinants operative in microbial [38,59,60,67,89,90], mammalian [117,122,172], fungal [180,181] and insect [246] enzymes have been ascertained ( Table 3). As may be anticipated, the majority of residues clusters within the heme-binding core domain encompassing the bundle of helices D, E, I and L [247], amino acids at positions 268, 393 and 400 being 89 to 100% conserved.…”

Section: Conclusion and Future Prospectsmentioning

confidence: 99%

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Control by Substrate of the Cytochrome P450-Dependent Redox Machinery: Mechanistic Insights

Hlavica¹

2007

CDM

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Based on initial studies with bacterial CYP101A1, a popular concept emerged predicting that substrate-induced low-to-high spin conversion of P450s is universally associated with shifts of the midpoint potential to a more positive value to maximize rates of electron transfer and metabolic turnover. However, evaluation of the plethora of observations with pro- and eukaryotic hemoproteins suggests a caveat as to generalization of this principle. Thus, some P450s are inherently high-spin, so that there is no need for a supportive substrate-triggered impulse to electron flow. With other enzymes, high-spin content is not consonant with reductive activity, and spin transition as such is not essential to sustaining substrate oxidation. Also, with certain proteins the low-spin conformer is reduced as swift as the high-spin entity. Moreover, there is not regularly a linear relationship between high-spin level and anodic shift of the reduction potential. Similarly, in given cases turnover may proceed despite insignificant or even lacking substrate-provoked alterations in the redox behaviour. Thus, folding of the disparate and sometimes conflicting data into a harmonized overall picture is a lingering problem. Apart from direct perturbation of the electrochemical properties, substrate docking may entail changes in enzyme conformation such as to favour productive complexation with redox partners or modulate electron transfer conduits within preformed donor/acceptor adducts, resulting in elevated ease of flow of reducing equivalents. Substrate-steered ordering of the oligomeric aggregation state of P450s is likely to impose steric constraints on heterodimers, causing one component to more readily align with electron carriers. Careful uncovering of electrochemical mechanisms in these systems will be fruitful to tailoring of novel bioenergetic machines and redox chains via redox-inspired protein engineering or molecular Lego, capable of generating products of interest or degrading toxic pollutants. Finally, availability of P450 nanobiochips for high-throughput screening of substrate libraries might expedite drug development.

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Section: Studies With Highly Purified and Recombinant P450 Systems Thmentioning

confidence: 82%

Section: Conclusion and Future Prospectsmentioning

confidence: 99%

Control by Substrate of the Cytochrome P450-Dependent Redox Machinery: Mechanistic Insights

Hlavica¹

2007

CDM

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“…It seems noteworthy that suicidal inactivation of P-450 2B4 through pretreatment of rabbits with allylisopropylacetamide has been previously detected to be associated with a loss of selective histidines responsible for electron transfer from cytochrome b & to the oxyferrous enzyme [42]. Similarly, mutation experiments have shown that His-163 in cytochrome P-450 1A2 serves in catalytic functions associated with cytochrome b & [43]. Unfortunately, we were unable to identify at least some of the critical histidines, owing to instability of the carbethoxylated material.…”

Section: Impact Of Derivatization Of P-450 2b4 On Nad(p)h-dependent Ementioning

confidence: 98%

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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“…Finally, imidazole (IM) was selected because of its well-known role in substrate-enzyme interactions within proteolytic and esterolytic enzymes [38,48]. It has been reported that an histidine residue present in the active site of CYP1A2 enzyme, the main enzyme responsible for the metabolism of CAF, plays a key role in its catalytic activity [49]. IM is generally considered to act as a moderate σ-donor and a weak π-acceptor, with σ-donor and π-acceptor abilities in between saturated amines, such as ammonia, and unsaturated amines, such as pyridine [50].…”

Section: Selection Of Binding Unit To Form Specific Interactions With...mentioning

confidence: 99%

Imidazole-Based Monomer as Functional Unit for the Specific Detection of Paraxanthine in Aqueous Environments

2022

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In the context of personalized medicine, the paraxanthine-to-caffeine ratio is an accepted standard for the optimization of the dose-response effect of many pharmaceuticals in individual patients. There is a strong drive towards the development of cheaper and portable devices for the detection of biomarkers, including paraxanthine and caffeine, which requires materials with high binding efficiency and specificity. We designed a recognition unit specific for paraxanthine which can discriminate molecules with small structural differences and can be used to increase the sensitivity of sensors. A number of functional units were screened by nuclear magnetic resonance for their ability to form specific binding interactions with paraxanthine in water and negligible interactions with its structural analogue caffeine. Imidazole was identified as the unit showing the most promising results and its two polymerizable derivatives were evaluated by isothermal titration calorimetry to identify the best monomer. The data suggested that 4-vinylimidazole was the most promising unit forming specific and strong binding interaction with paraxanthine. The calorimetry experiments allowed also the determination of the thermodynamic parameters of all interactions and the association constant values. Optimization of polymerization protocols in water, achieving high monomer conversions and chemical yields, demonstrate the suitability of the selected functional monomer for polymer preparations, targeting the detection of paraxanthine in aqueous environments.

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Essential Role of His163 of Cytochrome P450 1A2 in Catalytic Functions Associated with Cytochrome b5

Cited by 26 publications

References 0 publications

Control by Substrate of the Cytochrome P450-Dependent Redox Machinery: Mechanistic Insights

Control by Substrate of the Cytochrome P450-Dependent Redox Machinery: Mechanistic Insights

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

Imidazole-Based Monomer as Functional Unit for the Specific Detection of Paraxanthine in Aqueous Environments

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