Purification and physicochemical properties of starch phosphorylase from young banana leaves

Starch phosphorylase from young banana leaves has been purified to homogeneity, as tested by disc polyacrylamide gel electrophoresis at various pHs and gel concentrations, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, immunodiffusion, and immunoelectrophoresis, using the techniques of ammonium sulfate fractionation, DEAE-cellulose chromatography, and filtration through Sephadex G-100 and Sephadex G-200. The molecular weight of the enzyme is found to be 45000 as determined by gel filtration chromatography over Sephadex G-200. The enzyme showed a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis having the molecular weight 55000. The enzyme contains eight SH groups per mol of the enzyme. Unlike other 1,4-alpha-glucan phosphorylases, no evidence is found for the presence of pyridoxal 5'-phosphate as a prosthetic group of the enzyme. Of the various amino acids tested, only aromatic amino acids inhibited the enzyme activity. ADP, AMP, and 3',5'-AMP did not produce any effect on the enzyme activity whereas ATP and UDP-glucose proved to be inhibitors. The enzyme utilized starch, amylose, and glycogen as primers with equal efficiency whereas dextrin, amylopectin, maltotriose, and maltose were less effective as primers. Schardinger dextrin, cellulose, or sucrose could not be utilized as a primer. The enzyme showed absolute specificity for glucose 1-phosphate as a substrate, and this could not be replaced by glucose-6-phosphate, fructose-6-phosphate, fructose 1,6-bisphosphate, or ribose 5-phosphate.