1. Threonine aldolase was purified about 200-fold in 10% yield from Clostridium pasteurianum and its properties were examined. The final preparation gave three bands after ionophoresis on polyacrylamide gel. 2. The purified enzyme was shown to produce glycine and acetaldehyde in stoicheiometric amounts from threonine. The reverse reaction was demonstrated qualitatively. 3. The enzyme has a broad pH optimum at 6.5–7.0. 4. The enzyme is highly specific for l-threonine. 5. The enzyme is completely inhibited by 1mm concentrations of hydroxylamine and semicarbazide. Activity is decreased to 20% of the original by treatment with cysteine plus mercaptoethanol; most of the loss is regained on incubation with pyridoxal phosphate. It is concluded that pyridoxal phosphate is a prosthetic group. 6. The relationship between velocity and substrate concentration is atypical but indicates a Km value of 0.42mm. 7. The enzyme was demonstrated in several other strictly anaerobic bacteria.

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