Cyclic 3',5'-Nucleotide Phosphodiesterase Activities in Neurospora crassa

Two molecular species of repressible extracellular phosphodiesterases showing cyclic 2',3'and cyclic 3',5'-nucleotide phosphodiesterase activities were detected in mycelial culture media of wild-type Neurospora crassa and purified. The two molecular species were found to be monomeric and polymeric forms of an enzyme constituted of identical subunits having molecular weights of 50,000. This enzyme had the same electrophoretic mobility as repressible acid phosphatase. The enzyme designated repressible cyclic phosphodiesterase showed pH optima of 3.2 to 4.0 with a cyclic 3',5'-AMP substrate and 5.0 to 5.6 with a cyclic 2',3'AMP substrate. Repressible cyclic phosphodiesterase was activated by MnCl2 and CoCl2 with cyclic 2',3'-AMP as substrate and was slightly activated by MnCI2 with cyclic 3',5'-AMP. The enzyme hydrolyzed cyclic 3',5'and cyclic 2',3'nucleotides, in addition to bis-p-nitrophenyl phosphate, but not certain 5'-and 3'nucleotides. 3'-GMP and 3'-CMP were hydrolyzed less efficiently. Mutant strains Al (nuc-J) and Bi (nuc-2), which cannot utilize RNA or DNA as a sole source of phosphorus, were unable to produce repressible cyclic phosphodiesterase. The wild type (74A) and a heterocaryon between strains Al and Bi produced the enzyme and showed growth on orthophosphate-free media containing cyclic 2',3'AMP or cyclic 3',5'-AMP, whereas both mutants showed little or no growth on these media.