Kinetic properties of purified sheep lung microsomal NADH-cytochrome b5 reductase

P450 monooxygenases (P450ome) of the model white rot fungus Phanerochaete chrysosporium

Phanerochaete chrysosporium, the model white rot fungus, has been the focus of research for the past about four decades for understanding the mechanisms and processes of biodegradation of the natural aromatic polymer lignin and a broad range of environmental toxic chemicals. The ability to degrade this vast array of xenobiotic compounds was originally attributed to its lignin-degrading enzyme system, mainly the extracellular peroxidases. However, subsequent physiological, biochemical, and/or genetic studies by us and others identified the involvement of a peroxidase-independent oxidoreductase system, the cytochrome P450 monooxygenase system. The whole genome sequence revealed an extraordinarily large P450 contingent (P450ome) with an estimated 149 P450s in this organism. This review focuses on the current status of understanding on the P450 monooxygenase system of P. chrysosproium in terms of pre-genomic and post-genomic identification, structural and evolutionary analysis, transcriptional regulation, redox partners, and functional characterization for its biodegradative potential. Future research on this catalytically diverse oxidoreductase enzyme system and its major role as a newly emerged player in xenobiotic metabolism/degradation is discussed.

Cytochrome b₅ reductase-cytochrome b₅ as an active P450 redox enzyme system in Phanerochaete chrysosporium: atypical properties and in vivo evidence of electron transfer capability to CYP63A2

Two central redox enzyme systems exist to reduce eukaryotic P450 enzymes, the P450 oxidoreductase (POR) and the cyt b₅ reductase-cyt b₅. In fungi, limited information is available for the cyt b(5) reductase-cyt b(5) system. Here we characterized the kinetic mechanism of (cyt b₅r)-cyt b₅ redox system from the model white-rot fungus Phanerochaete chrysosporium (Pc) and made a quantitative comparison to the POR system. We determined that Pc-cyt b₅r followed a "ping-pong" mechanism and could directly reduce cytochrome c. However, unlike other cyt b₅ reductases, Pc-cyt b₅r lacked the typical ferricyanide reduction activity, a standard for cyt b₅ reductases. Through co-expression in yeast, we demonstrated that the Pc-cyt b₅r-cyt b₅ complex is capable of transferring electrons to Pc-P450 CYP63A2 for its benzo(a)pyrene monooxygenation activity and that the efficiency was comparable to POR. In fact, both redox systems supported oxidation of an estimated one-third of the added benzo(a)pyrene amount. To our knowledge, this is the first report to indicate that the cyt b₅r-cyt b₅ complex of fungi is capable of transferring electrons to a P450 monooxygenase. Furthermore, this is the first eukaryotic quantitative comparison of the two P450 redox enzyme systems (POR and cyt b₅r-cyt b₅) in terms of supporting a P450 monooxygenase activity.

FT-IR spectroscopy in diagnosis of diabetes in rat animal model

In recent years, Fourier Transform Infrared (FT-IR) spectroscopy has had an increasingly important role in the field of pathology and diagnosis of disease states. In the current study, FT-IR spectroscopy together with cluster analysis were used as a diagnostic tool in the discrimination of diabetic samples from control ones in rat kidney plasma membrane apical sides (brush-border membranes), liver microsomal membranes and Extensor digitorum longus (EDL) and Soleus (SOL) skeletal muscle tissues. A variety of alterations in the spectral parameters, such as frequency and signal intensity/area was observed in diabetic tissues and membranes compared to the control samples. Based on these spectral variations, using cluster analysis successful differentiation between diabetic and control groups was obtained in different spectral regions. The results of this current study further revealed the power and sensitivity of FT-IR spectroscopy in precise and automated diagnosis of diabetes.

Rapid monitoring of diabetes-induced lipid peroxidation by Fourier transform infrared spectroscopy: Evidence from rat liver microsomal membranes

Increased oxidative stress is the consequence of either enhanced reactive oxygen species (ROS) production or attenuated ROS scavenging capacity, resulting in tissue damage that in most instances is assessed by the measurement of lipid peroxides. In the current study, diabetes-induced lipid peroxidation in rat liver microsomal membranes was investigated by Fourier transform infrared (FT-IR) spectroscopy at different temperatures. The olefinic (CH) band at 3012 cm-1 was used to probe diabetes-induced lipid peroxidation. The intensity and area values of this band of diabetic samples were found to be increased significantly (P<0.05) compared with nondiabetic samples. The increase in olefinic band intensity is attributed mainly to the lipid peroxidation end products. The results of the FT-IR study were found to be in agreement with biochemical studies that revealed a significant increase in malondialdehyde levels of diabetic samples compared with control samples (P<0.05) using the thiobarbituric acid test.

Development and validation of a spectrophotometric assay for measuring the activity of NADH: cytochrome b5 reductase in human tumour cells

As part of an 'enzyme-directed' approach to bioreductive drug development, we have measured the activity of NADH: cytochrome b5 reductase (B5R) in human cancer cell lines in order to assess the role of this enzyme in activating bioreductive drugs, and thus in influencing the cytotoxicity of these compounds. At present, there is no validated assay reported in the literature for measuring the activity of B5R in tumour cells, and current measurements have assumed that the enzyme activity can be measured either as the NADH-dependent reduction of cytochrome c or as the non-dicoumarol-inhibitable activity in the DT-diaphorase assay. Using p-hydroxymercuribenzoate (pHMB) as an inhibitor of B5R, we have quantified the contribution of B5R to the NADH-dependent reduction of cytochrome c and to the overall reduction of cytochrome c in the DT-diaphorase assay. In the former we found that residual uninhibited activity remained in the presence of pHMB, in some cases accounting for up to 60% of the total reduction of cytochrome c. Thus, simply measuring the NADH-dependent reduction of cytochrome c consistently overestimated B5R activity. We also found that the non-dicoumarol-inhibitable activity in the DT-diaphorase assay underestimated B5R activity, especially in cell lines with high DT-diaphorase activity. Therefore, we have developed a spectrophotometric assay for measuring B5R activity as the pHMB-inhibitable NADH-dependent reduction of cytochrome c. This has been used to measure the B5R activity of a panel of 22 human tumour cell lines, in which we found 7-fold and 3-fold variations in activity expressed per cell or per mg protein respectively.

Purification and characterization of cytochrome b5 reductase from the house fly, Musca domestica

NADH-cytochrome b5 reductase (b5R) from the house fly was purified through solubilization of microsomes with Triton X-100 followed by DEAE, carboxylmethyl and 5'-ADP affinity column chromatography. Yields of 9% with a 320-fold increase in NADH-ferricyanide reductase specific activity and 2% with a 76-fold increase in NADH-cytochrome b5R specific activity were obtained. Two forms of b5R, a major form with the apparent molecular mass of 31 kDa and a minor form of 33 kDa, were obtained. Both forms of purified b5R could reduce cytochrome b5 and both could use NADH or NADPH as an electron donor, although NADH was more efficient. Kinetics of the b5R activities were also studied. The 31-kDa b5R consists of integral of 291 amino acids with the NH2-terminal sequence of Thr-Ala-Arg-Leu-Arg-Thr-Leu-Ile-Asp-Ala. An antiserum developed against the 31-kDa b5R recognized both forms of b5R. Using this polyclonal antiserum as a probe, immunologically reactive proteins were found in microsomes from five species of Diptera, mouse and rat liver but not in spider mites nor insects from other orders.