Purification and properties of 3-hexulose phosphate synthase and phospho-3-hexuloisomerase from Methylococcus capsulatus

Purification and properties of 3-hexulosephosphate synthase from Methylomonas M 15

3-Hexulosephosphate synthase, the first enzyme of the ribulose monophosphate cycle, was purified 15-fold from methanol-grown Methylomonas M 15. The purification procedure involved chromatography on DEAE-cellulose, Sephadex G-75, and DEAE-Sephadex A-50. The purified enzyme was more than 95% pure as judged by analytical polyacrylamide gel electrophoresis. The molecular weight was calculated to be 43000 from sedimentation equilibrium experiments. Electrophoresis in sodium dodecylsulfate gels gave a single band corresponding to a molecular weight of 22000. The enzyme catalyzes specifically the condensation formaldehyde with ribulose 5-phosphate to yield D-arabino-3-hexulose 6-phosphate. The Km values were found to be 1.1 mM for formaldehyde and 1.6 mM for ribulose 5-phosphate. A bivalent cation is essential for activity and stability of the enzyme, Mg2+ and Mn2+ serve best for this purpose. The optimum of pH for enzyme activity is 7.5--8.0.

The autotrophic growth of Micrococcus denitrificans on Methanol

Ribulose bisphosphate carboxylase is present at a high specific activity in extracts of methanol-grown Microccus denitrificans. Enzymic and physiological evidence indicates that, during growth on methanol, the ribulose bisphosphate cycle is the route of carbon assimilation.

The carbon assimilation pathways of Methylococcus capsulatus, Pseudomonas methanica and Methylosinus trichosporium (OB3B) during growth on methane

d-arabino-3-Hexulose 6-phosphate was prepared by condensation of formaldehyde with ribulose 5-phosphate in the presence of 3-hexulose phosphate synthase from methane-grown Methylococcus capsulatus. The 3-hexulose phosphate was unstable in solutions of pH greater than 3, giving a mixture of products in which, after dephosphorylation, allulose and fructose were detected. A complete conversion of d-ribulose 5-phosphate and formaldehyde into d-fructose 6-phosphate was demonstrated in the presence of 3-hexulose phosphate synthase and phospho-3-hexuloisomerase (prepared from methane-grown M. capsulatus). d-Allulose 6-phosphate was prepared from d-allose by way of d-allose 6-phosphate. No evidence was found for its metabolism by extracts of M. capsulatus, thus eliminating it as an intermediate in the carbon assimilation process of this organism. A survey was made of the enzymes involved in the regeneration of pentose phosphate during C(1) assimilation via a modified pentose phosphate cycle. On the basis of the presence of the necessary enzymes, two alternative routes for cleavage of fructose 6-phosphate are suggested, one route involves fructose diphosphate aldolase and the other 6-phospho-2-keto-3-deoxygluconate aldolase. A detailed formulation of the complete ribulose monophosphate cycle of formaldehyde fixation is presented. The energy requirements for carbon assimilation by this cycle are compared with those for the serine pathway and the ribulose diphosphate cycle of carbon dioxide fixation. A cyclic scheme for oxidation of formaldehyde via 6-phosphogluconate is suggested.