Enzymatic synthesis and properties of 8-bromoguanylic acid oligomers

Abstract

1. 1. Ribonuclease T1 (EC 2.7.26) was found to act on 8-bromoguanosine 2′,3′-cyclic phosphate. The K m for 8-bromoguanosine 2′,3′-cyclic phosphate was 13.3 · 10 −3 M which was about 3 times greater than that for guanosine 2′,3′-cyclic phosphate. 2. 2. 8-Bromoguanylic acid oligomers consisting of up to four nucleotide units were synthesized by ribonuclease T1 from 8-bromoguanosine 2′,3′-cyclic phosphate. The yields were 41.2 %, 9.8 % and 4.4 % for dimer, trimer and tetramer, respectively. 3. 3. Dimer 8-bromoguanylyl-8-bromoguanylic acid synthesized by ribonuclease T1 was completely digested by the same enzyme to mononucleotide. Specific chemical degradation after removal of terminal phosphate of dimer by periodate followed by treatment with lysine yielded 8-bromoguanosine 3′-monophosphate. These results clearly demonstrated that the nature of phosphodiester linkage in the dimer was 3′–5′. 4. 4. Hypochromicities in absorption spectra of dimer and trimer of 8-bromoguanylic acid were 19.6 % and 31.6 %, respectively. The oligomers exhibited quite different modes of optical rotatory dispersion from the monomer. These results suggest that there were strong mutual interactions between bases in the oligomers different from the usual “stacked” configuration.