May act during starch breakdown to convert small oligosaccharides into larger molecules upon which starch phosphorylase can act, or may change the structure of starch molecules and grain architecture by modifying chain length, or may generate from starch and glucose oligosaccharides which can serve either as primers for new starch phosphoenzyme. Transfers a segment of a (1->4)-alpha-D-glucan to a new position in an acceptor, which may be glucose or a (1->4)-alpha-D-glucan. Present in leaves, stems, roots, and stolons but is most abundant in developing and mature tubers. Belongs to the disproportionating enzyme family.