Glycine synthesis and degradation. The figure shows a schematic representation of glycine synthesis and degradation. SHMTs are the two serine hydroxymethyltransferase isoforms that catalyze the synthesis of glycine from serine, a reaction coupled with the conversion of tetrahydrofolate (THF) to 5,10-methylene THF. AMT, aminomethyltransferase; DLD, dihydrolipoamide dehydrogenase; GCSH, glycine cleavage system protein H and GLDC, glycine dehydrogenase, are components of the multiple-enzyme glycine cleavage system, the major pathway for glycine degradation.