Cytochrome c peroxidase
Encyclopedia
Cytochrome c peroxidase, or CCP is a water-soluble heme
-containing enzyme
of the peroxidase
family that takes reducing equivalents from cytochrome c
and reduces hydrogen peroxide
to water:
Cytochrome c peroxidase can react with hydroperoxides other than hydrogen peroxide, but the reaction rate is much slower than with hydrogen peroxide.
It was first isolated from baker's yeast
by R. A. Altschul, Abrams, and Hogness in 1940, though not to purity. The first purified preparation of yeast CCP dates to Takashi Yonetani and his preparation by ion exchange chromatography
in the early 1960s. The X-ray structure
was the work of Thomas Poulos and coworkers in the late 1970s.
The yeast enzyme is a monomer of molecular weight 34,000, containing 293 amino acids, and contains as well a single noncovalently bound heme
b. Unusual for proteins, this enzyme crystallizes when dialysed
against distilled water. More so, the enzyme purifies as a consequence of crystallization, making cycles of crystallization an effective final purification step.
Much like catalase
, the reaction of cytochrome c peroxidase proceeds through a three-step process, forming first a CCP-compound I and then a CCP-compound II:
CCP in the resting state has a ferric
heme, and, after the addition of two oxidizing equivalents from a hydroperoxide, it becomes an enzyme of formal oxidation state V. However, both low-temperature magnetic susceptibility measurements and Mössbauer spectroscopy show that the iron in CCP-compound I is a +4 ferryl iron, and not in oxidation state V. The other salient feature of CCP-compound I is a long-lived free-radical, whose signal suggests a species other than the porphyrin free-radicals of other peroxidase compound I species. Early on it was recognized to be an organic free-radical, with the bulk of evidence now linking it to the side-chain of the tryptophan
residue (Trp-191).
Unlike most peroxidases, CCP-compound I is fairly long-lived, decaying to CCP-compound II with a half-life at room temperature of 40 minutes to a couple hours.
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...
-containing enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
of the peroxidase
Peroxidase
Peroxidases are a large family of enzymes that typically catalyze a reaction of the form:For many of these enzymes the optimal substrate is hydrogen peroxide, but others are more active with organic hydroperoxides such as lipid peroxides...
family that takes reducing equivalents from cytochrome c
Cytochrome c
The Cytochrome complex, or cyt c is a small heme protein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins. Cytochrome c is a highly soluble protein, unlike other cytochromes, with a solubility of about 100 g/L and is an...
and reduces hydrogen peroxide
Hydrogen peroxide
Hydrogen peroxide is the simplest peroxide and an oxidizer. Hydrogen peroxide is a clear liquid, slightly more viscous than water. In dilute solution, it appears colorless. With its oxidizing properties, hydrogen peroxide is often used as a bleach or cleaning agent...
to water:
- CCP + H2O2 + 2 ferrocytochrome c + 2H+ → CCP + 2H2O + 2 ferricytochrome c
Cytochrome c peroxidase can react with hydroperoxides other than hydrogen peroxide, but the reaction rate is much slower than with hydrogen peroxide.
It was first isolated from baker's yeast
Baker's yeast
Baker's yeast is the common name for the strains of yeast commonly used as a leavening agent in baking bread and bakery products, where it converts the fermentable sugars present in the dough into carbon dioxide and ethanol...
by R. A. Altschul, Abrams, and Hogness in 1940, though not to purity. The first purified preparation of yeast CCP dates to Takashi Yonetani and his preparation by ion exchange chromatography
Chromatography
Chromatography is the collective term for a set of laboratory techniques for the separation of mixtures....
in the early 1960s. The X-ray structure
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
was the work of Thomas Poulos and coworkers in the late 1970s.
The yeast enzyme is a monomer of molecular weight 34,000, containing 293 amino acids, and contains as well a single noncovalently bound heme
Heme
A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...
b. Unusual for proteins, this enzyme crystallizes when dialysed
Dialysis (biochemistry)
In biochemistry, dialysis is the process of separating molecules in solution by the difference in their rates of diffusion through a semipermeable membrane, such as dialysis tubing....
against distilled water. More so, the enzyme purifies as a consequence of crystallization, making cycles of crystallization an effective final purification step.
Much like catalase
Catalase
Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it catalyzes the decomposition of hydrogen peroxide to water and oxygen...
, the reaction of cytochrome c peroxidase proceeds through a three-step process, forming first a CCP-compound I and then a CCP-compound II:
- CCP + ROOH → CCP-compound I + ROH + H2O
- CCP-compound I + e- + H+ → CCP-compound II
- CCP-compound II + e- + H+ → CCP
CCP in the resting state has a ferric
Ferric
Ferric refers to iron-containing materials or compounds. In chemistry the term is reserved for iron with an oxidation number of +3, also denoted iron or Fe3+. On the other hand, ferrous refers to iron with oxidation number of +2, denoted iron or Fe2+...
heme, and, after the addition of two oxidizing equivalents from a hydroperoxide, it becomes an enzyme of formal oxidation state V. However, both low-temperature magnetic susceptibility measurements and Mössbauer spectroscopy show that the iron in CCP-compound I is a +4 ferryl iron, and not in oxidation state V. The other salient feature of CCP-compound I is a long-lived free-radical, whose signal suggests a species other than the porphyrin free-radicals of other peroxidase compound I species. Early on it was recognized to be an organic free-radical, with the bulk of evidence now linking it to the side-chain of the tryptophan
Tryptophan
Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...
residue (Trp-191).
Unlike most peroxidases, CCP-compound I is fairly long-lived, decaying to CCP-compound II with a half-life at room temperature of 40 minutes to a couple hours.