Structure et activité de la polynucléotide phosphorylase d'Escherichia coli: une espèce à faible poids moléculaire

A polynucleotide phosphorylase with a molecular weight of 100,000 has been isolated from Escherichia coli Q13 mutant and partially purified. This mutant is particularly rich in this low molecular species which can, however, also be found in small proportion in wild strains of E. coli B and K12. Low molecular weight polynucleotide phosphorylase catalyzes only one of the reactions catalyzed by native polynucleotide phosphorylase (molecular weight 200,000), i. e. the phosphoro‐lysis of polyribonucleotides, and is unable to polymerize nucleoside diphosphates. However, in so far as the phosphorolysis reaction is concerned, there are some marked differences between the 100,000 polynucleotide phosphorylase and the 200,000 enzyme isolated from wild strains: reaction only with short chains polymers, higher requirement for Mg ++ ions, non‐lineartity of the reaction as a function of protein concentration. The Q13 mutant also contains a polynucleotide phosphorylase with a molecular weight of 200,000 but this enzyme is markedly different from the enzyme isolated from wild strains: in particular, it requires Mn ++ for the polymerization reaction and has a higher K m for poly A in the phosphorolysis; for this latter reaction Mg ++ and not Mn ++ is required. The oligomeric structure of polynucleotide phosphorylase and the relation between structure and activities is discussed.