Enzyme mannose 6-phosphate isomerase

These enzymes vary widely in secondary and tertiary structure.1273 Mannose-6-phosphate isomerase is a 45 kDa Zn2+-containing monomer. The larger 65 kDa L-fucose isomerase, which also acts on D-arabinose, is a hexameric Mn2+-dependent enzyme.1273 L-Arabinose isomerase of E. coli, which interconverts arabinose and L-ribulose, is a hexamer of 60-kDa subunits128 while the D-xylose isomerase of Streptomyces is a tetramer of 43-kDa subunits.129 The nonenzymatic counterpart of the isomerization catalyzed by the enzyme is the base-catalyzed Lobry deBruyn-Alberda van Ekenstein transformation (Eq. 13-25).130... 

There is no obvious pattern in the metal ion requirements of enzymes that catalyze proton transfer at carbon. For example, mannose 6-phosphate isomerase [85] is a metalloenzyme while triosephosphate isomerase [86] and glucose 6-phosphate... 

GDP-Man regeneration system starting from Man-l-P has been report by Wong s gcoup(9). As the Fru-6-P is inexpensive to obtain, we developed a new regeneration padiway from Fru-6-P with all recombinant enzymes. As shown in Scheme 4, the cycle comprises of three key enzymes D-mannose-6-phosphate isomerase (PMI, EC 5.3.1.8), phosphomannomutase (PMM, EC 5.4.2.S) and... 

Tissue was homogenised with an equal volume of buffer (2 ml Tris-HCl (pH 8.0), 0.1 ml mercaptoethanol, 10 g sucrose, and 25 mg NADP per 100 ml H2O - adjusted to pH 7.2 with HCl). Electrophoresis was performed on cellulose acetate plates (Titan III Helena Laboratories). A preliminary survey of 42 enzymes detected four enzyme loci, coding for four different enzyme systems that were polymorphic and consistently resolvable. These enzymes were used for the analysis and were as follows (abbreviation and enzyme commission number in parentheses) hexokinase (HK, E.C. 2.7.1.1), mannose-6-phosphate isomerase (MPI, E.C. 5.3.1.8), 6-phosphogluconate dehydrogenase (6PGD, E.C. 1.1.1.44), and phosphoglucose isomerase (PGI, E.C. 5.3.1.9). 

Therefore, glucose, mannose, and fructose can all be in equilibrium with the same enediol. This isomerization process occurs in biochemical reactions near pH 7 for several aldoses and ketoses in enzyme-catalyzed reactions. The isomerization of glucose and fructose occurs by way of their 6-ph osphate esters and is catalyzed by glucose 6-phosphate isomerase. The equilibrium constant for the formation of fructose 6-phosphate from glucose 6-phosphate is approximately 0.3. This reaction is one of the initial steps in glycolysis. 

This zinc-dependent enzyme [EC 5.3.1.8] (also known as phosphomannose isomerase, phosphohexoisomerase, and phosphohexomutase) catalyzes the interconversion of D-mannose 6-phosphate and o-fructose 6-phosphate. 

GDP-mannose pyrophosphorylase (GMP, EC 2.7.7.13). The recombinant bifimctional PMI/GMP (phosphomannose isomerase/GDP-D-mannose pyrophosphorylase) from Helicobacter pylori has been cloned and overexpressed in E. coli (21), The bifunctional enzyme PMI/GMP catalyzes both the first and third steps of GDP-D-mannose biosynthesis from D-fructose-6-phosphate. In addition, PMM of H. pylori was also cloned and overexpressed (21), The system was coupled with a truncated al,2-mannosyltransferase (ManT catalytic domain, Saccharomyces cerevisiae) to synthesize the mannosyloligosaccharides (not published). 

Glucose-6-phosphate is converted to fructose-6-phos-phate in the presence of a phosphoglucose isomerase. The enzyme was discovered and purified from muscle where it was separated from a phosphomannose isomerase, which catalyzes the conversion of mannose-6-... 

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