title: Formation and reorientation of glucose 1,6-bisphosphate in the PMM/PGM reaction: transient-state kinetic studies.
abstract: The interconversion of glucose 1-phosphate and glucose 6-phosphate, catalyzed by Pseudomonas aeruginosa phosphomannomutase/phosphoglucomutase, has been studied by transient-state kinetic techniques. Glucose 1,6-bisphosphate is formed as an intermediate in the reaction, but an obligatory step in the catalytic cycle appears to be the formation of an enzyme-glucose 1,6-bisphosphate complex that is not competent to form either glucose 1-phosphate or glucose 6-phosphate directly. We suggest that during the lifetime of this complex the glucose 1,6-bisphosphate intermediate undergoes the 180 degrees reorientation that is required for completion of the catalytic cycle. The formation of glucose 1,6-bisphosphate from glucose 1-phosphate is in rapid equilibrium relative to the rest of the reaction, where K(eq) = 0.14. In the opposite direction, glucose 1,6-bisphosphate is formed from glucose 6-phosphate with a rate constant of 12 s(-)(1), and the reverse step occurs with a rate constant of 255 s(-)(1). The interconversion of the productive and nonproductive glucose 1,6-bisphosphate complexes occurs with a rate constant of 64 s(-)(1) in one direction and 48 s(-)(1) in the other direction. Glucose 1,6-bisphosphate remains associated with the enzyme during reorientation. Isotope trapping studies indicate that it partitions to form glucose 1-phosphate or glucose 6-phosphate 14.3 times more frequently than it dissociates from the enzyme.
authors.affiliation: Department of Biochemistry, University of Missouri, Columbia, Missouri 65211, USA.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Naught
authors.forename: Peter A
authors.initials: PA
authors.lastname: Tipton
mesh_terms: D000818:Animals; D002250:Carbon Radioisotopes / Q000378:metabolism; D002384:Catalysis; D018360:Crystallography, X-Ray; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives* / Q000737:chemistry* / Q000378:metabolism; D007700:Kinetics; D009097:Multienzyme Complexes / Q000737:chemistry* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000201:enzymology; D010733:Phosphoglucomutase / Q000737:chemistry* / Q000378:metabolism; D010766:Phosphorylation; D017875:Phosphotransferases (Phosphomutases) / Q000737:chemistry* / Q000378:metabolism; D011550:Pseudomonas aeruginosa / Q000201:enzymology*; D011817:Rabbits; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D002250:Carbon Radioisotopes; D009097:Multienzyme Complexes; D011994:Recombinant Proteins; D019298:Glucose-6-Phosphate; C016473:glucose-1,6-bisphosphate; D017875:Phosphotransferases (Phosphomutases); D010733:Phosphoglucomutase; C052799:phosphomannomutase