Glycine decarboxylase multienzyme complex. Purification and partial characterization from pea leaf mitochondria.

Area of Science:

• Biochemistry
• Plant Molecular Biology

Background:

• The glycine cleavage system is crucial for amino acid metabolism in plants.
• Understanding its components is key to deciphering metabolic pathways.

Purpose of the Study:

• To purify and characterize the P, H, and T proteins of the glycine cleavage system from pea leaf mitochondria.
• To investigate the functional interactions and cofactor requirements of these proteins.

Main Methods:

• Protein purification using SDS-PAGE and gel filtration.
• Enzyme reconstitution assays with purified proteins.
• Kinetic analysis (Km determination).
• Immunopurification and Western blotting.

Main Results:

• Purified P, H, and T proteins have distinct molecular weights (98,000, 15,500, and 45,000 Da).
• P protein exists as a homodimer (210,000 Da).
• Reconstituted system requires pyridoxal phosphate, tetrahydrofolate, NAD+, and dithiothreitol for glycine oxidation.
• Stoichiometric production of CO2, methylamine-H protein intermediate, and methylenetetrahydrofolate.
• H protein acts as a co-substrate with an apparent Km of 2.2 µM.
• P and H proteins catalyze glycine carboxyl-14CO2 exchange.
• L protein shows similarities to lipoamide dehydrogenase of the pyruvate dehydrogenase complex.

Conclusions:

• The P, H, and T proteins are essential components of the pea leaf glycine cleavage system.
• The system's activity is dependent on specific cofactors and co-substrates.
• Evidence suggests a potential shared lipoamide dehydrogenase component between glycine and pyruvate dehydrogenase complexes.