Polynucleotide phosphorylase polymerization

They did find that these compounds behaved kinetically as competitive inhibitors of polymerization of the normal substrates e.g., guanosine 5 -diphosphate. These authors suggested that the successful completion of the polynucleotide phosphorylase reaction requires that the nucleotide be capable of assuming the anti conformation. Also, Kapuler and Reich (53) have found that both 8-bromo- and 8-oxoguanosine 5 -triphosphates are very poor substrates in the E. coli RNA polymerase reaction and are competitive inhibitors with respect to guanosine 5 -triphosphate as a substrate. 

Polymerization activity of proteinoid or polynucleotide-phosphorylase has been compared in ADP solution at pH 8.5 48). The results show that the activity of the neutral proteinoid is approximately 20 times lower than that of the enzyme, and the lower molecular-weight fraction of the proteinoid has negligible activity. The polymerization by polynucleotide-phosphorylase is increased approximately three times when Leuchs polylysine is supplied, polylysine and enzyme yield a heterogeneous solution 48). 

Liebl, V., Novak, V., Bejsovcova, L., Masinovskij, Z., Oparin, A. I. Polymerization of radioactive adenosine diphosphate by polynucleotide-phosphorylase or by proteinoids in microsystems, in Origin of Life Proceedings of the Second ISSOL Meeting, the Fifth ICOL Meeting (ed.) Noda, H., p. 363, Japan, Bus. Cent. Acad. Soc. Japan 1978... 

Polynucleotide phosphorylase. An enzyme that polymerizes ribonucleotide diphosphates. No template is required. 

Another enzyme of possible significance in this metabolic area is polynucleotide phosphorylase, which was first viewed as primarily a catalyst for RNA s3mthesis. The reaction involved is the reversible polymerization of ribonucleotide 6 -diphosphates with the concomitant liberation of inorganic phosphate (G17). It is quite possible that the biological role of this enzyme is the reverse reaction, i.e., the production of nucleoside diphosphates from RNA. 

The reaction of 5 -amino-5 -deoxyadenosine with trimetaphosphate affords the 5 -Af-triphosphate (23). When (23) is employed as substrate with glucose in the hexokinase-catalysed reaction, the 5 -AT-diphosphate (24) is obtained the latter is cleaved by snake venom phosphodiesterase to the 5 -phosphoramidate, and hydrolyses in acid to the amino-nucleoside. It does not appear to be polymerized by polynucleotide phosphorylase. In this context it is noteworthy that uridine 5 -5-thiopyrophosphate (25) is a competitive inhibitor for polynucleotide phosphorylase from E. coli, but not a substrate, and that the 5 -S-thiotriphosphates (26) and (27) show neither substrate nor inhibitory properties for RNA polymerase or DNA polymerase I, respectively. However, (23) can be polymerized using the latter enzyme, showing that the introduction of a 5 -heteroatom does not completely exclude these modified nucleotides as substrates for the polymerizing enzymes. 

Several years ago, Chakrabarti et al. " described for the first time such a polymerization of RNA inside DMPC vesicles by polynucleotide phosphorylase. In these experiments, ADP was added externally to the enzyme-containing vesicles (this enzymatic reaction does not require template nucleic acids for initiation) and incubated at 23°C, the main phase transition temperature of DMPC. Because of these gel-to-liquid crystalline transitions of the bilayer, the vesicles could take up ADP from the external milieu, and the enzyme could produce poly (A). On the other hand, the enzyme could not leak out because of its size. Similar experiments were also carried out in our group by Walde et al. Here, the vesicles consisted of a single-chain amphiphile (oleic acid/oleate) that forms vesicles at a pH of about 8.0. ADP was shown to permeate across the oleic acid/oleate membrane and was incorporated inside the vesicles by polynucleotide phosphorylase to poly(A). 

A number of polynucleotides containing atypical bases have been prepared during the past year either by polymerizing ribonucleoside diphosphates with polynucleotide phosphorylase or by polymerizing... 

Poly(7-deazaguanylic acid) has been prepared by polymerization of 7-deaza-guanosine 5 -diphosphate using polynucleotide phosphorylase from Micrococcus luteus, and its ability to form duplexes with complementary polynucleotides compared with that of poly(G). It is cleaved by ribonuclease T1 and also by nuclease SI, showing that unlike poly(G), it forms no selfstructure in aqueous solution. ... 

Polynucleotide phosphorylase, which polymerizes ribonucleoside diphosphates (NDP) to form RNA and Pj, was used in the laboratory to synthesize polyribonucleotides that were useful in determining the genetic code. Why is it unlikely that this enzyme synthesizes RNA in the cell Suggest how the cell uses this enzyme. 

Oparin and coworkers [125,126] have studied the enzymic polymerization of ADP by polynucleotide phosphorylase (PNPase) and Mg ions in coacervates in an attempt to construct primitive forms of precellular structures. Walde et al. [127] have investigated this enzymic ADP polymerization in AOT reversed micellar solutions instead of coacervates. The PNPase-catalyzed synthesis of poly(A) (polyadenylic acid) in the AOT reversed micelles was carried out by mixing two reversed micellar solutions, one containing ADP and the other containing the enzyme. 

Polynucleotide phosphorylase catalyzes the formation of RNA from nucleoside diphosphates, with phosphate as the second product. This reaction is reversible, and at the normal cellular concentration of inorganic phosphate and nucleoside diphosphates the equilibrium condition favors phosphorolysis of RNA rather than polymerization. Although the addition of primer RNA stimulates RNA formation, it does not specify the nucleotide sequence of the product. Polynucleotide phosphorylase, therefore, appears to be involved in the degradation of cellular RNA rather than in its formation. 

We have studied the enzymatic polymerization of ADP in a sodium bis(2-ethylhexyl) sulfosuccinate, AOT, reversed micellar system [3]. This enzymatic polymerization by polynucleotide phosphorylase(PNPase) and Mg ion was greatly different from the general aspect of the enzy-... 

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