Alteration of processive mechanism of native polynucleotide phosphorylase by fixation to solid matrix.

Native $\text{E. coli}$ polynucleotide phosphorylase can be covalently bound to BrCN activated Sepharose. The Sepharose bound enzyme retains 70 % of its initial activity in polymerisation of nucleoside diphosphate. The Km of the enzyme for the polymerisation reaction in comparison to the soluble enzyme is not affected by its linkage to a solid matrix. The phosphorolysis of an hexanucleotide by the Sepharose-bound enzyme is not affected either. However, the rate of phosphorolysis of a long chain polynucleotide is dramatically altered. The Km values for poly(A) or poly(U) are increased by two orders of magnitude. The decrease of affinity for polymeric substrate is accompanied by a significant modification of the known processive mechanism characteristic of the native soluble enzyme.