The glycine cleavage system is also known as the glycine decarboxylase complex or GCS. The system is a series of enzymes that are triggered in response to high concentrations of the amino acid glycine

Glycine

Glycine is an organic compound with the formula NH2CH2COOH. Having a hydrogen substituent as its 'side chain', glycine is the smallest of the 20 amino acids commonly found in proteins. Its codons are GGU, GGC, GGA, GGG cf. the genetic code.Glycine is a colourless, sweet-tasting crystalline solid...

. The glycine cleavage system is composed of four proteins: the T-protein, P-protein, L-protein, and H-protein. They do not form a stable complex, so it is more appropriate to call it a "system" instead of a "complex"

Components

Name	EC number	Function
T-protein (GCST or AMT Aminomethyltransferase Aminomethyltransferase is an enzyme that catabolizes the creation of methylenetetrahydrofolate. It is part of the glycine decarboxylase complex.... )		aminomethyltransferase Aminomethyltransferase Aminomethyltransferase is an enzyme that catabolizes the creation of methylenetetrahydrofolate. It is part of the glycine decarboxylase complex....
P-protein (GLDC)		glycine dehydrogenase (decarboxylating) or just glycine dehydrogenase Glycine dehydrogenase (decarboxylating) Glycine dehydrogenase [decarboxylating], mitochondrial also known as glycine cleavage system P protein or glycine decarboxylase is an enzyme that in humans is encoded by the GLDC gene.- Reaction :... .
L-protein (GCSL or DLD Dihydrolipoamide dehydrogenase Dihydrolipoamide dehydrogenase , also known as dihydrolipoyl dehydrogenase, mitochondrial, is an enzyme that in humans is encoded by the DLD gene. DLD is a flavoprotein enzyme that degrades lipoamide, and produces dihydrolipoamide.... )		known by many names, but most commonly dihydrolipoyl dehydrogenase
H-protein (GCSH GCSH Glycine cleavage system H protein, mitochondrial is a protein that in humans is encoded by the GCSH gene.- Function :The enzyme system for cleavage of glycine , which is confined to the mitochondria, is composed of 4 protein components: P protein , H protein Glycine cleavage system H protein,... )		is modified with lipoic acid Lipoic acid Lipoic acid , also known as α-lipoic acid and Alpha Lipoic Acid is an organosulfur compound derived from octanoic acid. LA contains two vicinal sulfur atoms attached via a disulfide bond and is thus considered to be oxidized...  and interacts with all other components in a cycle of reductive methylamination (catalysed by the P-protein), methylamine transfer (catalysed by the T-protein) and electron transfer (catalysed by the L-protein).

Function

In plants the glycine cleavage system is coupled to serine hydroxymethyltransferase

Serine hydroxymethyltransferase

Serine hydroxymethyltransferase is an enzyme which plays an important role in cellular one-carbon pathways by catalyzing the reversible, simultaneous conversions of L-serine to glycine and tetrahydrofolate to 5,10-methylenetetrahydrofolate...

 to give an overall reaction of:

2 glycine + NAD⁺ + H₂O → serine + CO₂ + NH₃ + NADH + H⁺

This reaction, and by extension the glycine cleavage system, is required for photorespiration

Photorespiration

Photorespiration, or "'photo-respiration'", is a process in plant metabolism by which RuBP has oxygen added to it by the enzyme , instead of carbon dioxide during normal photosynthesis. This is the beginning step of the Calvin-Benson cycle...

 in C₃ plants. Together the proteins involved in these reactions comprise about half the proteins in mitochondria from spinach

Spinach

Spinach is an edible flowering plant in the family of Amaranthaceae. It is native to central and southwestern Asia. It is an annual plant , which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions...

 and pea

Pea

A pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking...

 leaves

Leaves

-History:Vocalist Arnar Gudjonsson was formerly the guitarist with Mower, and he was joined by Hallur Hallsson , Arnar Ólafsson , Bjarni Grímsson , and Andri Ásgrímsson . Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times...

.