Comparison of batch and chromatographic assays of cyclic nucleiotide phosphodiesterases

An improved method for the assay of cyclic nucleotide phosphodiesterases (CNPases) is described in which residual 3H-cAMP or 3H-cGMP is separated from products by chromatography on thin layers of PEI-cellulose. Comparison of CNPase activity in crude or purified kidney enzyme assayed by the PEI-cellulose method with a batch anion-exchange resin method showed serious underestimation of activity by the latter method. The batch method underestimated CNPase activity by 34-82%. The error was due to substantial binding of nucleosides (adenosine and guanosine) to the resin, which is assumed not to occur by those using this method.