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Polynucleotide phosphorylase has been purified from the cyanobacterium Nostoc sp. MAC. The enzyme requires a divalent cation such as Mg2+, has a pH optimum of 10·5 and catalyses the polymerization of ADP into polynucleotide in a primer-independent reaction at a rate of 2 mol min−1 (mg protein)−1. It has an apparent native M r of 215000–240000. Non-denaturing polyacrylamide activity gels reveal a heterogeneous pattern of active bands similar to those previously observed with the corresponding enzyme from Micrococcus luteus, while SDS-denaturing activity gels reveal a single band of activity of M r 91000 in both crude extracts and the most highly purified fraction. Activity has also been demonstrated in a cetyltrimethyl-ammonium bromide non-denaturing activity gel. By analogy with other known polynucleotide phosphorylases, the Nostoc enzyme is probably a trimer of the 91000-M r subunit.
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