Glycine Formation via Threonine and Serine Aldolase. Its Interrelation with the Pyruvate Formate Lyase Pathway of One‐carbon Unit Synthesis in Clostridium kluyveri

14C‐labeling experiments with growing Clostridium kluyveri have shown that two pathways each are operative for glycine and one‐carbon unit synthesis: about two‐thirds of the cell's glycine is formed from threonine and one third from serine; serine simultaneously yields about a quarter of the cell's C1‐units, while the remaining three‐quarters are derived from CO2via the pyruvate carboxyl group. The key enzymes, threonine aldolase and pyruvate formate lyase as well as serine aldolase interrelating glycine and C1‐unit synthesis, could be demonstrated in cell‐free lysates in activities sufficient to account for the anabolic requirements during growth. The substrate specificity, cofactor requirements and Km values indicate that threonine aldolase and serine aldolase are two separate, constitutive and pyridoxal phosphate dependent enzymes.