Configuration of substrate and products of N-acetylneuraminate pyruvate-lyase from Clostridium perfringens.

To characterize the true substrate for aldolase from Clostridium perfringens (optimum pH = 7.2) several experiments were carried out wherein the substrate Neu5Ac was generated in situ at pH 5.4 by the action of sialidase on its substrate Neu5Ac(alpha, 2 leads to 3) lactose. The alpha-anomer formed in this reaction was found to be split by aldolase at this pH into ManNAc and pyruvate. beta-Neu5Ac as such was not converted at pH 5.4. However, when it was first mutarotated until the equilibrium mixture alpha:beta = 7.2:92.8 was obtained, it could be split. Inhibition experiments suggested that Neu5Ac was bound to the enzyme in a conformation that strongly resembled that of its alpha-anomer. The open chain form of ManNAc which arose after the action of aldolase preferentially formed the alpha-anomer followed by a fast mutarotation.