Team:Copenhagen/Project/Cytochrome

Cytochromes




What makes them special

Background information: Cytochromes p450 is one of the largest gene superfamilies coding for enzymes present in the genomes in all biological kingdoms [1]. The enzymatic activities of these proteins are extremely diverse with activity in biotransformation of drugs, bioconversion of xenobiotics, biosynthesis of compounds as steroids, fatty acids, eicosanoids, fat soluble vitamins and bile acids. Furthermore, cytochrome p450’s are involved in the conversion of alkanes, terpenes and aromatic compounds as well as degradation of herbecides and insecticides [1].

The P450 catalytic cycle in hydroxylation

Cytochromes p450 is one of the largest gene superfamilies coding for enzymes present in the genomes in all biological kingdoms [1]. The enzymatic activities of these proteins are extremely diverse with activity in biotransformation of drugs, bioconversion of xenobiotics, biosynthesis of compounds as steroids, fatty acids, eicosanoids, fat soluble vitamins and bile acids. Furthermore, cytochrome p450’s are involved in the conversion of alkanes, terpenes and aromatic compounds as well as degradation of herbecides and insecticides [1].

We will exploit this activity of cytochromes p450 in the bioconversion of xenobiotics to neutralize damaging medical residues in waste water.

Cytochromes p450 are defined as heme-thiolate proteins featuring a particular spectral signature at 450 nm, thus the name [2]. Despite the label as cytochromes, these proteins are not involved in electron transfers, but act as monooxygenases in a wide range of reactions such as epoxidation, N-dealkylation, O-dealkylation, S-oxidation and hydroxylation [3].

We will focus on the hydroxylating property of the cytochromes, which is also the defining reaction for these enzymes. The reductive activation of molecular oxygen reduces one of the oxygen atoms to a molecule of water, as the other is inserted into the substrate [2].

RH + NAD(P)H + O2 + H+ -> ROH + NAD(P)+ + H2O

A key donor of electrons for the reduction of molecular oxygen is the NADPH dependent cytochrome p450 reductase (CPR). This protein shuttles electrons from NADPH through the FAD and FMN- coenzymes into the iron of the prosthetic heme group of cytochrome p450 [4].

References

[1] F. Hannemann, A. Bichet, K. M. Ewen, R. Bernhardt: Cytochrome p450 systems – biological variations of electron transport chains. Biochemica et Biophysica Acta 1770 (2007) 330 - 344
[2] Paul R. Ortiz de Montellano. Hydrocarbon Hydroxylation by Cytochrome P450 Enzymes. Chem Rev. 2010 February 10; 110(2): 932
[3] http://www.anaesthetist.com/physiol/basics/metabol/cyp/Findex.htm
[4] T. Laursen, K. Jensen,B. L. Møller: Conformational changes of the NADPH dependent cytochrome P450 reductase in the course of electron transfer to cytochromes P450. Biochemica et Biophysica Acta 1814 (2011) 132-138