136] Enzymatic synthesis of polyguanylic acid and copolymers containing guanylic acid

Abstract

Publisher Summary This chapter discusses enzymatic synthesis of polyguanylic acid and copolymers containing guanylic acid. The synthesis of high molecular weight polyguanylie acid proceed with great difficulty under conditions where the other homopolymers are readily formed. Polyguanylic acid can be obtained without a primer when the concentration of substrate GDP and Mg ++ are very low but in the presence of a large amount of enzyme. Thus, with 1 m M GDP and polynucleotide phosphorylase extracted from Azotobacter vinelandii, high molecular weight poly G is formed. When polymerization of GDP, catalyzed by highly purified polynucleotide phosphorylase isolated from Escherichia coli , is made at 60° and in the presence of Mn ++ instead of Mg ++ , the reaction proceeds readily; the procedure is quite reproducible. The polyguanylic acid thus obtained is fairly homogeneous and has a high molecular weight. The only limiting factor is the enzyme. Polynucleotide phosphorylase isolated from Escherichia coli and purified to at least DEAE-Sephadex step can synthesize the polyguanylic acid under the conditions described in the chapter, as far as the yield and the properties of the polymer are concerned. At a lower temperature, polynucleotide phosphorylase isolated from Micrococcus lysodeikticus can also synthesize poly G in the presence of a primer. Enzymatic synthesis of copolymers in the presence of high ratio of GDP also presents some difficulty whether in the presence or the absence of primer. The ratio of guanylic acid to other nucleotides incorporated into the copolymers is always higher than the ratio of GDP to other nucleoside diphosphatcs in the input pool.