CyP450

Ⅰ. Introduction
Cytochrome p450 is one kind of protein with hemin,
it has billion-year history and is widespread in the biosphere. Cytochrome p450 enzyme system as a functional unit composed of many components. Include two kinds of cytochrome (cytochrome p450 and cytochrome b5), two kinds of flavoprotein (NADPH-cytochrome p450 reductase and NADPH-cytochrome b5 reductase), phospholipids, of which the cytochrome p450 and cytochrome p450 reductase is most important.
Figure B and C are CYp450 2C9’s active site. In figure C which is combine with substrate, but it’s hardly observe conformational changes . In short ,under the Induced - fit mechanism, different cyp450 may get variable conformational changes .
Ⅱ. Structure
The known structures of liver microsomal CYP proteins published in the last six years show relatively conserved overall structure.
Cytochrome P450 enzymes family has similar unique folding structure and the same oxidative active site (HEM), from the N end to C terminal incl. α-helix structure that contains A, B, C, D, F, E, G, H, I, J, K, L, and similar β-sheet structure.
Integrated structures of several cytochrome P450 shown: heme groups are limited to the terminal spiral helix I and adjacent helix L; Cys which close to the active center reacts with the amido- of the neighboring main chain forming two hydrogen bonds; long helix I forms the heme pocket wall, contains the characteristic amino acid sequence; highly conserved acidic residues, Thr located in the active site, participate in catalysis .
Ⅳ. Function
P450 enzymes are ubiquitous hemecontaining mono-oxygenases and involved in a number of vital processes including carcinogenesis and drug metabolism as well as the biosynthesis of steroid hormones and fat-soluble vitamin metabolism and the conversion of polyunsaturated fatty acids to biologically active molecules.
5. Substrate Oxidate
High iron oxygen intermediates [P • Fe (IV) = O], which not only have a single electron and a positive charge, but also can provide active oxygen atoms, then made it possible to transfer oxygen atoms into inert C-H bond, under mild conditions to achieve hydroxylation of hydrocarbons.
This figure shows Conformational changes in the CYP3A4 structures (between free CYP3A4 in gray and CYP3A4 in complex with erythromycin in black) induced by binding of a large substrate (erythromycin, in sticks) are localized to the F/Gsegment. The shift of the F/F’ loop lead to the dramatic increase in the active site volume
Cytochrome p450 is the terminal oxidase of p450 enzyme system, and is a key component enzyme. With iron protoporphyrin base as prosthetic group, it is a single chain protein of cytochrome b family . It is named because of its similar structure to Hemoglobin , and after it’s reduction state react with CO has a photoabsorption peak at 450nm. Cytochromes p450 (CYPs) are one of the most intensively studied enzymes thanks to their ability to act in many processes including biosynthesis of important regulatory molecules as e.g. steroid hormones or taking part in metabolism of foreign substances (xenobiotics) incl. drugs of human use.
P-Fe(II)-O2＋e-＋H→ P-Fe(III)-O-OH＋H2O
4. The formation of highly reactive inter-mediates oxygenated iron
P•Fe(III)-O-OH＋H+→[P•Fe(IV)＝O]+＋H2O This process is the restrictive procedures
It’s cyp450’s active centre
Ⅲ. Substrate recognition and combi-nation---- Induced - fit mechanism
Through the Induced - fit mechanism,the cytochrome P450 identify the substrate with six substrate recognition sites (SRS) incl.: B 'helix (SRS1); helix G and part of helix F (SRS2 and SRS3); part of helix I (SRS4), helix K’sβ2 connection area (SRS6), and the β hairpin district (SRS5). SRS is a flexible protein regions, it’s able to move to the substrate, under the effectof the "induced – fit"mechanism ,itcombine with the substrate, and catalysis the subsequent reaction.
2. HEM combine with oFra Baidu bibliotekygen molecules
P-Fe(III)＋O2＋e-→ P-Fe(II)-O2 or P-Fe(III)＋H2O2 → P-Fe(III)-O-OH＋H+
3. The formation of Fe (III) - compounds with hydrogen peroxide (here get another e- )
Ⅴ. Conclusions
In a summary, it is necessary to point out that our knowledge of active site properties of human liver micro-somal cytochromes P450 is far from complete. With researches of cytochrome P450 structure and function, and the further understanding of enzyme structure-function relationships, it will promote the development of drug design and enzyme chemistry.
As a heme-containing mono-oxygenases ,here we analyze its Catalytic oxidation process
1.Ferric reduction
Electrons from the FMN, Trp-574 Mobile to Pro-382 -Gln-387 peptide, then to the cysteine(Cys-400) ligands across bonding orbital directly to the iron of HEM, hence the ferric reducted .