alpha-Glucan phosphorylases catalyze the glucosyl transfer from alpha-D-glucosyl fluoride to oligosaccharides.

Regulated and nonregulated phosphorylases were found to catalyze in a slow, orthophosphate dependent reaction the direct transfer of the glucosyl residue from alpha-D-glucosyl fluoride to an oligosaccharide primer. The enzyme catalyzed formation of the glucosyl residue requires stereospecific protonation of alpha-D-glucosyl fluoride by a Brønstedt acid. The results are interpreted by a mechanism whereby phosphate acts as a proton shuttle and the cofactor pyridoxal 5'-phosphate is required to promote the acid-base function of phosphate.