Abstract
Summary: Polynucleotide phosphorylase activity was demonstrated in free-living and the symbiotic bacteroid forms of Rhizobium meliloti and in free-living Rhizobium japonicum. Crude extracts of R. meliloti f-28 catalysed the polymerization of 3.0 μmol ADP (mg protein)-1 h-1. The polynucleotide phosphorylase activity of symbiotic R. meliloti was about 50% of that of free-living R. meliloti and remained almost constant throughout the development of the nodules. Partially-purified fractions of free-living R. meliloti f-28 catalysed the polymerization of ribonucleoside diphosphates, the phosphorolysis of synthetic homopolymers and natural heteropolymers, and the β-phosphate exchange reaction. The enzyme had a pH optimum of 8.0 and had an obligatory requirement for Mg2+ for maximum activity. The phosphorylase was not highly primer-dependent, had low specificity for guanosine-containing substrates, and exhibited cooperative-type kinetics.
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