SEPARATION AND CHARACTERIZATION OF A NOVEL ISOENZYME OF CYCLIC-NUCLEOTIDE PHOSPHODIESTERASE FROM RAT CEREBRUM

Anion-exchange chromatography on a Mono-Q column of the supernatant fr action, after ultracentrifugation, from a homogenate of rat cerebrum, prepared under isotonic conditions in the presence of protease inhibit ors, yielded a novel isoenzyme of cyclic nucleotide phosphodiesterase (PDE) with properties unlike those of known PDEs. The isoenzyme was in sensitive to stimulation by Ca2+/calmodulin and cyclic GMP, and it hyd rolyzed both cyclic AMP and cyclic GMP with KM values of 0.109 +/- 0.0 08 mu M and 1.78 +/- 0.04 mu M, respectively. The ratio of V-max of hy drolysis of cyclic GMP to that of cyclic AMP was 1.90 +/- 0.07. Nicard ipine (PDE I inhibitor), SK&F 94120 (PDE III inhibitor), rolipram (PDE IV inhibitor) and zaprinast (PDE V inhibitor) had very weak inhibitor y effects on the PDE activity of the isoenzyme. These results suggest that the isoenzyme is a novel and previously unreported species of PDE , which we tentatively designate PDE VIII.