HORT640 - Metabolic Plant Physiology
Ammonia Assimilation and Recycling
Glycine decarboxylase complex
Glycine decarboxylase (GDC) is composed of 4 different component proteins that are referred to as P-, H-, T- and L-proteins.
The P-protein is a homodimer of 105 kDa peptides that binds the alpha-amino group of glycine through its pyridoxal-phosphate cofactor and catalyzes the decarboxylation of glycine in the presence of the H-protein (a monomer of 14 kDa).
The carboxyl group of glycine is released as CO2 and the remaining methylamine moiety is transferred onto the lipoamide arm of the H-protein.
The lipoamide-bound methylamine group is shuttled to the T-protein (a monomer of 41 kDa). The methylene carbon is transferred to THF (5,6,7,8-tetrahydropteroyl-polyglutamic acid) to produce N5N10N-methylene-5,6,7,8-tetrahydropteroyl-polyglutamic acid, and the amino nitrogen is released as NH3.
The L-protein (a dimer of 50 kDa) reoxidizes the dihydrolipoamide of the H-protein by the sequential reduction of FAD and NAD+ (Vauclare et al, 1996).
All of the proteins of the GDC complex are encoded by nuclear genes. The P-, H- and T- proteins are expressed predominantly in the leaf tissue, whereas the L-protein occurs in all tissues because it is also the component of other mitochondrial complexes (e.g. pyruvate decarboxylase complex) (Vauclare et al, 1996).
In pea, the transcription of the GDC genes was coordinated and occurred early with a peak in 7 d old plants at which time mitochondria are unable to oxidize glycine, implying posttranscriptional control (Vauclare et al, 1996).
Vauclare P, Diallo N, Bourguignon J, Macherel D, Douce R 1996 Regulation of the expression of the glycine decarboxylase complex during pea leaf development. Plant Physiol. 112: 1523-1530.
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