Sweet corn phosphorylase: purification and properties

Sweet corn 1,4-α-glucan phosphorylase was purified 190-fold to a near homogeneous state. The enzyme had a molecular weight of about 315,000 on Sephadex G-200 chromatography. The pyridoxal 5′-phosphate content was found to 1 mole per 140,000 g protein, suggesting that the enzyme is dimeric. On sucrose density gradient ultracentrifugation the sweet corn phosphorylase was dissociated to an active monomeric species with a molecular weight of 150,000 and a sedimentation coefficient of 8 S. The priming specificity of the sweet corn phosphorylase was investigated; maltose was not a primer and maltotriose was the smallest apparent primer. The Michaelis constants for the maltosaccharide series from maltopentaose to maltooctaose were determined. The effect of d-enzyme on the apparent priming specificity of the enzyme was investigated. Adenosine diphosphoglucose and 2,3-diphosphoglycerate were found to inhibit the enzyme activity.