An enzymatic tandem reaction is described in which the enzymes phosphorylase and Deinococcus geothermalis glycogen branching enzyme (Dg GBE) catalyze the synthesis of branched polyglucans from glucose-1-phosphate (G-1-P). Phosphorylase consumes G-1-P and polymerizes linear amylose while DR GBE introduces branching points on the alpha-(1 -> 6) positions by reshuffling short oligosaccharides. The resulting branched polyglucans have an unusually high degree of branching of 11%.