J. Biochem, 1977, Vol. 81, No. 4 899-909
© 1977 Japanese Biochemical Society
research-article |
Studies on the Priming Specificity of Polyribonucleotides of Azotobacter vinelandii Polynucleotide Phosphorylase1
Kobe Kaisei, Stella Maris College Aotani, Nada-ku, Kobe, Hyogo 657
The lag phase in the polymerization of ribonucleoside 5'-diphosphate by polynucleotide phosphorylase from Azotobacter vinelandii was found to be caused by a basic protein isolated from the crude enzyme preparation or by a synthetic basic polypeptide. Poly(A) formed during the lag phase was bound to added polylysine in a 1:1 ratio on a monomer basis. Preferential repression of polymerization of UDP was observed with polylysine and of ADP with polyarginine. These findings may explain why the polymerization of UDP is slower than that of ADP, and suggest that a lysine-rich area in the enzyme may act as a regulatory site. The so-called primer can thus be considered as an activator.
The lag phase in UDP polymerization caused by polylysine was eliminated by poly(U) or poly(C) and prolonged by poly(A), in a manner similar to that previously observed with the priming specificity. A lag phase was also caused by polylysine in the P1ADP exchange reaction, but not in poly(A) phosphorolysis. The effect of basic polypeptide on the nucleotidyl transferase activity of the enzyme indicates that the complete reaction of Azotobacter poly nucleotide phosphorylase is an exchange reaction, which includes polymerization and phosphorolysis. A complex, [polynucleotide phosphorylase-Mg2+-ribonucleoside 5' diphosphate], which the enzyme appears to form as a reactive intermediate, and a possible scheme for the priming specificity are described.
1This work was supported in part by Scientific Research Grants (No. 497071 and No. 738037) from the Ministry of Education, Science and Culture of Japan.