Methionine oxidation
Encyclopedia
Methionine oxidation is the oxidation
of the sulfur
of the amino acid
methionine
resulting in methionine sulfoxide or methionine sulfone. The sulfur-containing amino acids methionine and cysteine
are more easily oxidized than the other amino acids. Unlike oxidation of other amino acids, the oxidation of methionine can be reversed by enzymatic action, specifically by enzyme
s in the methionine sulfoxide reductase family of enzymes. The three known methionine sulfoxide reductases are MsrA
, MsrB
, and fRmsr. Oxidation of methionine results in a mixture of the two diastereomer
s methionine-S-sulfoxide and methionine-R-sulfoxide, which are reduced by MsrA and MsrB, respectively. MsrA can reduce both free and protein-based methionine-S-sulfoxide, whereas MsrB is specific for protein-based methionine-R-sulfoxide. fRmsr, however, catalyzes the reduction of free methionine-R-sulfoxide. Thioredoxin
serves to recycle by reduction some of the methionine sulfoxide reductase family of enzymes, whereas others can be reduced by metallothionein
.
Methionine sulfoxide increases with age in body tissues, which is believed to contribute to ageing
. Transgenic Drosophila
(fruit flies) that overexpress methionine sulfoxide reductase show extended lifespan
.
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
of the sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
of the amino acid
Amino acid
Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...
methionine
Methionine
Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...
resulting in methionine sulfoxide or methionine sulfone. The sulfur-containing amino acids methionine and cysteine
Cysteine
Cysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
are more easily oxidized than the other amino acids. Unlike oxidation of other amino acids, the oxidation of methionine can be reversed by enzymatic action, specifically by 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...
s in the methionine sulfoxide reductase family of enzymes. The three known methionine sulfoxide reductases are MsrA
MSRA (gene)
Peptide methionine sulfoxide reductase is an enzyme that in humans is encoded by the MSRA gene.-Further reading:...
, MsrB
MSRB2
Methionine-R-sulfoxide reductase B2, mitochondrial is an enzyme that in humans is encoded by the MSRB2 gene. The MRSB2 enzyme catalyzes the reduction of methionine sulfoxide to methionine.-Further reading:...
, and fRmsr. Oxidation of methionine results in a mixture of the two diastereomer
Diastereomer
Diastereomers are stereoisomers that are not enantiomers.Diastereomerism occurs when two or more stereoisomers of a compound have different configurations at one or more of the equivalent stereocenters and are not mirror images of each other.When two diastereoisomers differ from each other at...
s methionine-S-sulfoxide and methionine-R-sulfoxide, which are reduced by MsrA and MsrB, respectively. MsrA can reduce both free and protein-based methionine-S-sulfoxide, whereas MsrB is specific for protein-based methionine-R-sulfoxide. fRmsr, however, catalyzes the reduction of free methionine-R-sulfoxide. Thioredoxin
Thioredoxin
Thioredoxin is a class of small redox proteins known to be present in all organisms. It plays a role in many important biological processes. In humans, it is encoded by the TXN gene. Loss-of-function mutation of either of the two human thioredoxin genes is lethal at the four-cell stage of the...
serves to recycle by reduction some of the methionine sulfoxide reductase family of enzymes, whereas others can be reduced by metallothionein
Metallothionein
Metallothionein is a family of cysteine-rich, low molecular weight proteins. They are localized to the membrane of the Golgi apparatus...
.
Methionine sulfoxide increases with age in body tissues, which is believed to contribute to ageing
Ageing
Ageing or aging is the accumulation of changes in a person over time. Ageing in humans refers to a multidimensional process of physical, psychological, and social change. Some dimensions of ageing grow and expand over time, while others decline...
. Transgenic Drosophila
Drosophila
Drosophila is a genus of small flies, belonging to the family Drosophilidae, whose members are often called "fruit flies" or more appropriately pomace flies, vinegar flies, or wine flies, a reference to the characteristic of many species to linger around overripe or rotting fruit...
(fruit flies) that overexpress methionine sulfoxide reductase show extended lifespan
Life extension
Life extension science, also known as anti-aging medicine, experimental gerontology, and biomedical gerontology, is the study of slowing down or reversing the processes of aging to extend both the maximum and average lifespan...
.