[Quaternary structure of uridine phosphorylase from E. coli K-12].

Uridine phosphorylase was isolated from E. coli K-12 cells in a homogeneous state. The molecular mass of the enzyme as determined by gel filtration corresponds, approximately, to a hexamer made up of 27.5 kDa monomers. Evidence for the hexameric structure of uridine phosphorylase was obtained by electron microscopy with numerical treatment of the images. The six monomers within the enzyme molecule are arranged in two layers, three monomers in each, at the apices of a triangular antiprism with a point group symmetry of 32.