The glycine cleavage system (GCS) in bacteria is a critical multienzyme complex responsible for the catabolism of glycine, playing an important role in one-carbon metabolism and energy production. This system consists of four protein components: P-protein (glycine decarboxylase), T-protein (aminomethyltransferase), H-protein (a lipoate-containing carrier protein), and L-protein (dihydrolipoamide dehydrogenase). The process begins with glycine binding to the P-protein, where it undergoes decarboxylation and deamination, releasing CO? and ammonia. The remaining methylamine group is transferred to the H-protein as a one-carbon unit, which is then passed to tetrahydrofolate (THF) by the T-protein, forming 5,10-methylene-THF, a key intermediate in one-carbon metabolism. The L-protein regenerates the oxidized form of the H-protein by transferring electrons to NAD?, forming NADH. This pathway allows bacteria to efficiently utilize glycine as a carbon and nitrogen source while contributing to cellular one-carbon pools necessary for nucleotide and amino acid biosynthesis. The glycine cleavage system is particularly important in organisms that grow on glycine or serine as their primary energy source and is tightly regulated to maintain metabolic balance and prevent glycine toxicity.