title: Purification, properties and assay of D-ribulose 5-phosphate 3-epimerase from human erythrocytes.
abstract: A direct assay procedure is described for D-ribulose 5-phosphate 3-epimerase (EC 5.1.3.1) which exploits differences in the c.d. spectra of substrate and product. The enzyme has been purified from human erythrocytes and was resolved by gel filtration and sucrose-density-gradient centrifugation into a major component of apparent Mr 45 000 and a minor component of Mr 23 000. Electrophoresis in sodium dodecyl sulphate gave a single component corresponding to Mr 23 000. Kinetic and sucrose-density-gradient centrifugation data indicate dissociation of the dimeric form of the enzyme into monomers of low specific activity; substrate favours the active dimeric form of the enzyme. At concentrations of the enzyme where both forms of the enzyme are present initial velocity data yielded a Hill plot with an interaction coefficient of approx. 2.0, indicating co-operative binding of substrate under these conditions.
mesh_terms: D002238:Carbohydrate Epimerases / Q000302:isolation & purification; D002499:Centrifugation, Density Gradient; D002850:Chromatography, Gel; D002942:Circular Dichroism; D004912:Erythrocytes / Q000201:enzymology*; D006801:Humans; D007700:Kinetics; D008970:Molecular Weight; D013057:Spectrum Analysis
chemical_list: D002238:Carbohydrate Epimerases; C022553:ribulosephosphate 3-epimerase