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

Hlavica, Peter; Lehnerer, Michael; Eulitz, Manfred

doi:10.1042/bj3180857

Cited by 8 publications

(1 citation statement)

References 39 publications

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“…However, when measurements were carried out with saturating amounts of sixteen structurally distinct compounds such as aminopyrine, morphine, hexobarbital and others, the composite plot of percentage high-spin protein vs. rate of ferric enzyme reduction gave a scattergram with the two parameters being poorly (r 2 = 0.70) correlated [135]. Similar findings were made with CYP2B4 bearing chemically modified active-site histidine(s): While blockage of the residue(s) left OR association and degree of hexobarbital-controlled high-spin perturbation unaffected, chemical manipulation mitigated electron transfer by about 50 to 70% [136,137]. Moreover, only 40 to 60% of the amount of NADPH consumed in response to benzphetamine binding to the intact hemoprotein was shown to be accompanied by the formation of formaldehyde as the major metabolic product [126,138], which is close to the proportion of highspin heme ( Table 2).…”

Section: The Cyp2b Enzymesmentioning

confidence: 55%

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: The Cyp2b Enzymesmentioning

confidence: 55%

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

Hlavica¹

2007

CDM

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Residue 285 in Cytochrome P450 2B4 Lacking the NH2-Terminal Hydrophobic Sequence Has a Role in the Functional Association of NADPH–Cytochrome P450 Reductase

Schulze¹,

Tschöp²,

Lehnerer³

et al. 2000

Biochemical and Biophysical Research Communications

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Comparing the electronic properties and docking calculations of heme derivatives on CYP2B4

et al. 2008

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Cytochrome P-450 is a group of enzymes involved in the biotransformation of many substances, including drugs. These enzymes possess a heme group (1) that when it is properly modified induces several important physicochemical changes that affect their enzymatic activity. In this work, the five structurally modified heme derivatives 2-6 and the native heme 1 were docked on CYP2B4, (an isoform of P450), in order to determine whether such modifications alter their binding form and binding affinity for CYP2B4 apoprotein. In addition, docking calculations were used to evaluate the affinity of CYP2B4 apoprotein-heme complexes for aniline (A) and N-methyl-aniline (NMA). Results showing the CYP2B4 heme 4- and heme 6-apoprotein complexes to be most energetically stable indicate that either hindrance effects or electronic properties are the most important factors with respect to the binding of heme derivatives at the heme-binding site. Furthermore, although all heme-apoprotein complexes demonstrated high affinity for both A and NMA, the CYP2B4 apoprotein-5 complex had higher affinity for A, and the heme 6 complex had higher affinity for NMA. Finally, surface electronic properties (SEP) were calculated in order to explain why certain arginine residues of CYP2B4 apoprotein interact with polarizable functionalities, such as ester groups or sp ( 2 ) carbons, present in some heme derivates. The main physicochemical parameter involved in the recognition process of the heme derivatives, the CYP2B4 apoprotein and A or NMA, are reported.

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

Cited by 8 publications

References 39 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

Residue 285 in Cytochrome P450 2B4 Lacking the NH2-Terminal Hydrophobic Sequence Has a Role in the Functional Association of NADPH–Cytochrome P450 Reductase

Comparing the electronic properties and docking calculations of heme derivatives on CYP2B4

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