The glycine cleavage system catalyzes the degradation of glycine. The H protein shuttles the methylamine group of glycine from the P protein to the T protein. Is also involved in protein lipoylation via its role as an octanoyl/lipoyl carrier protein intermediate. Binds 1 lipoyl cofactor covalently. The glycine cleavage system is composed of four proteins: P, T, L and H. Belongs to the GcvH family.