Enzymes of KDO Metabolism

Studies of this enzyme (EC 5.3.1.13) were first reported by Volk,131-133 and later by Lim and Cohen.134 It is noteworthy that this enzyme reaction is reversible. The 41-fold purification of the enzyme from cells of Propionibacterium pentosaceum, using conventional procedures, has been reported.133 

The enzyme is susceptible to heavy-metal inactivation, so that the biochemical manipulations were performed in the presence of (ethylenedinitrilo)tetraacetate (EDTA). The KM for D-arabinose 5-phos- 

These circumstances became apparent to the authors when they attempted to study the formation of KDO 8-phosphate as catalyzed by purified bacterial extracts. These extracts did not catalyze the formation of KDO 8-phosphate from D-ribose 5-phosphate, but required D-arabinose 5-phosphate as the substrate Heath and Ghalambor29 showed that the KDO 8-phosphate synthetase reaction, observed in Pseudomonas extracts by Levin and Racker, is also catalyzed by extracts from Escherichia coli strains 0 111 B4 and J-5. Rick and Osborn136 showed that the KDO 8-phosphate synthetase from a Salmonella typhimurium mutant conditionally defective in cell-wall synthesis had a KM of 6 mM as compared to a KM of 170 pM for the enzyme from wild-type cells. 

A comprehensive study of KDO 8-phosphate synthetase has been reported by Ray.137 The author purified the enzyme 450-fold from crude extracts of Escherichia coli B cells. The synthetase has a molecular mass of 90,000 6,000 daltons and is composed of three identical subunits having an apparent molecular mass of32,000 4,000 daltons. Two pH optima were observed, one being at pH 4.0-6.0 in succinate buffer, and the other, at pH 9.0 in glycine buffer. The isoelectric point of the enzyme is 5.1. The enzyme has an apparent KM for D-arabinose 5-phosphate of 20 pM and an apparent KM for enolpyruvate phosphate of 6 pM. 

In a preliminary study, Berger and Hammerschmid138 showed that extracts from Escherichia coli 0 111 B4 contain an enzyme that cata- 

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