Interconversion of serine and glycine (PubMed:8505317, PubMed:24698160). (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + glycine + H2O = (6S)-5,6,7,8-tetrahydrofolate + L-serine Inhibited by tetrahydrofolate concentrations above 40 uM. One-carbon metabolism; tetrahydrofolate interconversion. Homotetramer (PubMed:24698160, PubMed:25619277, PubMed:9753690). Identified in complex with ABRAXAS2 and the other subunits of the BRISC complex, at least composed of ABRAXAS2, BRCC3/BRCC36, BABAM2 and BABAM1/NBA1 (PubMed:24075985). In eukaryotes there are two forms of the enzymes: a cytosolic one and a mitochondrial one. Belongs to the SHMT family.