A New Cyclic Phosphodiesterase Having a 3'-nucleotidase Activity from Escherichia Coli B. Ii. Further Studies on Substrate Specificity and Mode of Action of the Enzyme.

A number of phosphodiesterases which can hydrolyze ribonucleoside 2’, 3’-cyclic phosphates have been demonstrated in several biological materials (l-6). The preceding paper (7) presented evidence which strongly suggests the existence of a novel enzyme, designated temporarily as a cyclic phosphodiesterase, in the 78,000 x g supernatant of Escherichia coli B. At the same time a 3’-nucleotidase (EC 3.1.3.6) which accompanies the cyclic phosphodiesterase in parallel with the purification procedure was also found; neither activity had previously been reported in E. coli B. In this report, further studies on substrate specificity and mode of action of these two enzymes are described in detail. The conversion of uridine 2’) 3’.cyclic phosphate to uridine 3’-monophosphate by the cyclic phosphodiesterase was directly determined, and a special effort was made to see whether these two enzyme activities are present on the same active site. The results obtained show that both the cyclic phosphodiesterase and the 3’-nucleotidase have a strict substrate specificity. From kinetic analyses of these two activities, evidence is obtained that they occur on different sites.