Studies on polynucleotide phosphorylase of rhizobia and a new nucleoside diphosphatase of alfalfa and soybean nodules



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Polynucleotide phosphorylase was purified approximately 75-fold from extracts of Rhizobium meliloti F-28. The enzume was demonstrated to catalyze the polymerization of nucleoside diphosphates, the phosphorolysis of homo- and heteropolyribonucleotides, and the terminal phosphate exchange reactions. The polymerization and phosphorolysis reactions were characterized in respect to pH optimums, cation requirements, substrate preferences, reaction kinetics and an estimation of molecular weight. Polynucleotide phosphorylase activity was also determined in crude extracts of R. meliloti HP-31, LZ-26 and 3D0a1, strains ineffective in forming nodules, R. japonicum 705, a strain effective in the nodulation of soybean, and in the bacteroids (symbiotic R. meliloti F-28) of alfalfa nodules. Significant levels of phosphorylase activity was measured in all the extracts except those of R. meliloti 3D0a1. This organism was shown to contain a highly active phosphatase which masked the phosphorylase activity in the crude extracts. [...]