High impact information on CYB5

• Purified CYP2B4, reconstituted in the presence of NADPH-cytochrome P450 reductase and cytochrome b5, metabolized arachidonic acid, producing primarily EETs [1].
• Staining with a polyclonal antibody against pig liver cytochrome b5 reductase, which acts as one ubiquinone reductase in the plasma membrane, showed an increased expression of the enzyme in membranes from -E -Se rats [2].
• In erythrocytes, soluble cytochrome b5 functions in methemoglobin reduction [3].
• In addition, purified microsomal cytochrome P450 reductase and soluble cytochrome b5 reconstitute the activity of the porcine methionine synthase [3].
• It contains the heme in its cytochrome b5 structure, has no sulfite oxidase activity, and is reducible with dithionite but not with sulfite [4].

Biological context of CYB5

• The aim of this study was to search the porcine CYB5 gene for mutations, examine its expression, identify genetic polymorphisms, and study how a genetic variation in this enzyme translates into interindividual variation in androstenone levels in fat from pig testis [5].
• We have identified a single nucleotide polymorphism (SNP) (G --> T) at base 8 up-stream of ATG in the CYB5 5' untranslated region which is associated with a lower fat androstenone level [5].
• Furthermore, possible binding sites for cytochrome b5, the substrate CMP-Neu5Ac and a mononuclear iron centre were also identified [6].
• Studies of the reaction kinetics established that in the absence of cytochrome b5, methoxyflurane and benzphetamine are competitive inhibitors, and that in the presence of cytochrome b5, benzphetamine and methoxyflurane are two alternate substrates in competition for a single site on the same enzyme [7].
• Furthermore, it is also suggesting that cytochrome b5 electron transport system involves the reaction of delta 5-3 beta-hydroxysteroid dehydrogenase [8].

Anatomical context of CYB5

• Recent data has implicated an increased level of cytochrome b5 in the testes with the increased synthesis of the 16-androstene steroids [9].
• When the antibody to cytochrome b5 was treated with purified cytochrome b5 before addition to the microsomes, it did not inhibit methoxyflurane metabolism [10].
• This enzyme is a soluble cytochrome b5-dependent monooxygenase and has been purified to apparent homogeneity from pig submandibular glands by precipitation with N-cetyl-N,N,N-trimethylammonium bromide and fractionation on Q-Sepharose, Cibacron Blue 3GA-Agarose, Reactive Brown 10-Agarose, Hexyl-Agarose and Superose S.12 [11].
• Biochemical aspects of b-type cytochromes in swine cerebral microsomes were different from those of cytochrome b5 in liver microsomes, as well as the difference in absorption spectra [12].
• Terminal sequences of lysosome solubilized pig liver cytochrome b5 reductase [13].

Associations of CYB5 with chemical compounds

• Incubation of a purified and reconstituted 17 alpha-hydroxylase system, consisting of P-450(17 alpha,lyase), NADPH-P-450 reductase, cytochrome b5, and dilauroylphosphatidylcholine, with 7 alpha-thio-SL plus NADPH effected the complete degradation of the P-450(17 alpha,lyase) [14].
• Adrenal microsomal NADPH- and NADH-cytochrome c reductase activities and cytochrome b5 concentrations increased wih aging, but cytochrome P-450 concentrations were not significantly different in young and old guinea pigs [15].
• This indicates that electron transfer from flavin to cytochrome b5 proceeds in two successive one-electron steps [16].
• The two-domain structure of cytochrome b5 in deoxycholate solution [17].
• 0. In contrast, no reaction of As.- with ferrous cytochrome b5 could be detected by pulse radiolysis, whereas the oxidation of cytochrome b5 by As.- was observed by ascorbate-ascorbate oxidase method [18].

Other interactions of CYB5

• NADPH-cytochrome P-450 reductase gave a dynamic equilibrium of oxidation-reduction of cytochrome b5 in the presence of menadione (MK), the level of which depended on the concentration of O2 and superoxide dismutase [19].

Analytical, diagnostic and therapeutic context of CYB5

• As an initial step in analyzing this process, we used 5' and 3' RACE PCR procedures to isolate, clone and sequence the cDNAs for the membrane-bound and soluble forms of porcine cytochrome b5 [9].
• Titration with purified pig liver cytochrome b5, demonstrated a 4-fold maximum stimulation at a cytochrome b5 to a P-450 molar ratio of 1-2 [20].
• Expression of proteins responsible for these activities, aromatase (P450arom) and 17 alpha-hydroxylase/17,20-lyase (P450c17) cytochromes P450, reductase, and for the first time in ovarian tissues cytochrome b5, were examined by Western immunoblot and immunocytochemistry [21].
• The cytochrome b5 was determined to have an isoelectric point of 4.45 on analytical isoelectric focusing [22].
• Magnetic circular dichroism studies on microsomal aryl hydrocarbon hydroxylase: comparison with cytochrome b-5 and cytochrome P-450-cam [23].

References