Cytochrome: A Useful System

Mr. Amit Kumar Shukla, Asst. Professor, School of Agriculture Sciences, Career Point University, Kota


Introduction- Cytochromes are redox-active proteins containing a heme, with a central Fe atom at its core, as a cofactor. They are involved in electron transport chain and redox catalysis. They are classified according to the type of heme and its mode of binding.

Plant cytochrome : Cytochrome P450s (CYPs) are the largest enzyme family involved in NADPH- and/or O2-dependent hydroxylation reactions across all the domains of life. In plants and animals, CYPs play a central role in the detoxification of xenobiotics.

Location : In healthy cells, cytochrome c (Cyt c) is located in the mitochondrial intermembrane/intercristae spaces, where it functions as an electron shuttle in the respiratory chain and interacts with cardiolipin (CL).

Molecular weight : Cytochrome c (Cytc) comprises 104 amino acids and is a nuclear-encoded mitochondrial protein. This peripheral membrane protein is in spherical shape and has a molecular weight of 12,000 Da.

Biology : Cytochromes are proteins that contain heme as their prosthetic group and whose principal biological function, in the cells of animals, plants, and microorganisms, is electron transport.

Function : Cytochrome c is primarily known for its function in the mitochondria as a key participant in the life-supporting function of ATP synthesis. However, when a cell receives an apoptotic stimulus, cytochrome c is released into the cytosol and triggers programmed cell death through apoptosis.

Why it is called? Cytochromes were initially described in 1884 by MacMunn as respiratory pigments (myohematin or histohematin). In the 1920s, Keilin rediscovered these respiratory pigments and named them the cytochromes, or “cellular pigments”.

Types of cytochromes:-
There are three main types of cytochromes: A, B and C, with each main type having a subtype. Cytochromes A, B and C participate in the electron transfer during respiration and photosynthesis. Cytochrome P450, another cytochrome, contains one mole of heme and has a main role in detoxification. Cytochrome c is an electron carrying mitochondrial protein that is extremely efficient in transporting electrons. Unlike myoglobin and hemoglobin proteins, cytochrome c does not have the 6th position of the heme ring available to bind with ligands (Faustman et al., 1996).

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