Glycine cleavage system P-protein, alpha- and beta-subunits. This family consists of Glycine cleavage system P-proteins EC:126.96.36.199 from bacterial, mammalian and plant sources. The P protein is part of the glycine decarboxylase multienzyme complex EC:188.8.131.52 (GDC) also annotated as glycine cleavage system or glycine synthase. GDC consists of four proteins P, H, L and T. The reaction catalysed by this protein is: Glycine + lipoylprotein <=> S-aminomethyldihydrolipoylprotein + CO2. Alpha-beta-type dimers associate to form an alpha(2)beta(2) tetramer, where the alpha- and beta-subunits are structurally similar and appear to have arisen by gene duplication and subsequent divergence with a loss of one active site. The members of this CD are widely dispersed among all three forms of cellular life.