Mammalian mitochondrial and microsomal cytochromes b5 exhibit divergent structural and biophysical characteristics

Background: High amidoxime reductase activity is found in liver and fat tissue, although its composition in cells is unknown. Results: Amidoxime reductase is up-regulated during adipogenesis and requires MOSC2 and CYB5B. Conclusion: MOSC2 and CYB5B are essential components of the mitochondrial amidoxime reductase, and MOSC2 is important for lipogenesis. Significance: We suggest a role of MOSC2 in adipogenesis and fatty acid synthesis and as a potential novel drug target.

Section: Discussionmentioning

confidence: 99%

Amidoxime Reductase System Containing Cytochrome b5 Type B (CYB5B) and MOSC2 Is of Importance for Lipid Synthesis in Adipocyte Mitochondria

Neve

Nordling

Andersson

et al. 2012

“…The C-terminal mitochondrial leader sequence of CYB5B was also removed, but no affinity tag was included. Protein production and purification was carried out as previously described (21,22). Concentrations of CYB5R3 and CYB5B were measured with UV-visible spectroscopy (Cary 50 spectrophotometer) using the previously published extinction coefficients for CYB5R3 (⑀ 462 nm ϭ 10.4 mM Ϫ1 cm…”

Section: Methodsmentioning

confidence: 99%

Structure Guided Chemical Modifications of Propylthiouracil Reveal Novel Small Molecule Inhibitors of Cytochrome b5 Reductase 3 That Increase Nitric Oxide Bioavailability

Rahaman¹,

Reinders²,

Koes³

et al. 2015

“…2). One possible explanation for the residual activity could be the presence of an alternate electron donor, such as the recently described outer mitochondrial cytochrome b 5 , which is derived from a gene locus on chromosome 8 (45,46) and encodes for a protein of 16.3 kDa, slightly larger than microsomal cytochrome b 5 at 15.2 kDa and ϳ45% identical at the amino acid level. However, to date, there is no evidence for the interaction of outer mitochondrial cytochrome b 5 with the microsomal P450 system.…”

Section: Discussionmentioning

confidence: 99%

Defining the in Vivo Role for Cytochrome b5 in Cytochrome P450 Function through the Conditional Hepatic Deletion of Microsomal Cytochrome b5

Finn

McLaughlin

Ronseaux

et al. 2008

114

In vitro, cytochrome b 5 modulates the rate of cytochrome P450-dependent mono-oxygenation reactions. However, the role of this enzyme in determining drug pharmacokinetics in vivo and the consequential effects on drug absorption distribution, metabolism, excretion, and toxicity are unclear. In order to resolve this issue, we have carried out the conditional deletion of microsomal cytochrome b 5 in the liver to create the hepatic microsomal cytochrome b 5 null mouse. These mice develop and breed normally and have no overt phenotype. In vitro studies using a range of substrates for different P450 enzymes showed that in hepatic microsomal cytochrome b 5 null NADH-mediated metabolism was essentially abolished for most substrates, and the NADPH-dependent metabolism of many substrates was reduced by 50 -90%. This reduction in metabolism was also reflected in the in vivo elimination profiles of several drugs, including midazolam, metoprolol, and tolbutamide. In the case of chlorzoxazone, elimination was essentially unchanged. For some drugs, the pharmacokinetics were also markedly altered; for example, when administered orally, the maximum plasma concentration for midazolam was increased by 2.5-fold, and the clearance decreased by 3.6-fold in hepatic microsomal cytochrome b 5 null mice. These data indicate that microsomal cytochrome b 5 can play a major role in the in vivo metabolism of certain drugs and chemicals but in a P450-and substrate-dependent manner.Microsomal cytochrome b 5 is a 15.2-kDa hemoprotein, located in the endoplasmic reticulum with its obligate electron donor, cytochrome b 5 reductase. This protein is involved in fatty acid desaturation, reactivation of methemoglobin to hemoglobin, and electron transfer into the cytochrome P450 system (1-4).The role of cytochrome b 5 in cytochrome P450 monooxygenase reactions has been controversial for nearly 40 years (5, 6). Depending on the cytochrome P450 involved, the experimental conditions, and the substrate utilized, cytochrome b 5 has been shown to stimulate or inhibit cytochrome P450 reactions (2, 6). Indeed, in the case of cytochrome P450 CYP2B4, activity can be both stimulated or inhibited by the presence of the enzyme, depending on the concentration of cytochrome b 5 (7, 8). Cytochrome b 5 has been shown to affect the in vitro activities of a wide range of human P450s, such as CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, and CYP3A4, as well as the metabolism of an extensive number of commonly used drugs (9, 10). Although the mechanism(s) of the stimulatory effect of cytochrome b 5 on P450 metabolism appear complex, it is widely accepted that the P450 catalytic cycle involves the sequential transfer of two electrons from NADPH via P450 oxidoreductase (POR).2 Hildebrandt and Estabrook (5) concluded that cytochrome b 5 /cytochrome b 5 reductase was able to supply the second (rate-limiting) electron from NADH and possibly in a more rapid manner. However, recent data from Waskell et al. (8) suggest that cytochrome b 5 and POR are capable of reducing P450s at muc...