Cytochrome P-450 refers to a colored substance in the cell that absorbs light at around 450 nm within the visible spectrum. The word cyto means cell and chrome means color. The P in P-450 refers to pigment and the 450 refers to its wavelength.
Cytochrome is a cellular heme-containing protein. Its principal function is electron transport. Hemoglobin transports oxygen whereas cytochrome P-450 is a mono-oxygenase using one atom from oxygen and two electrons to oxidize chemical substrates.
In the early 1960s P-450 was thought to be one enzyme. Gonzales et al. isolated the first cDNA encoding a complete cytochrome P-450 protein. Since then dozens of different enzymes have been isolated. The P-450 cyto-chromes are ubiquitous enzymes found in microorganisms and throughout the plant and animal kingdoms. The mustard plant contains 249 active CYP genes and the rice plant has 324. The human cytochrome P-450 has 57 genes.
Cytochrome P-450 proteins are arranged into fami¬lies and subfamilies on the basis of percentage of amino acid sequence identity. Enzymes that share more than 40% identity are assigned to a particular family designated by an Arabic numeral, whereas those sharing more than 55% identity make up a subfamily designated by a letter.