Multiple forms of cyclic nucleotide phosphodiesterase in a murine adrenal cortex cell line (Y-1)

Abstract

Murine adrenal cortex tumor Y-1 cells contained both soluble and particulate forms of cyclic nucleotide phosphodiesterase (3′,5′-cyclic AMP 5′-nucleotide hydrolase, EC 3.1.4.17). The soluble forms of the enzyme comprised 80% of total cellular phosphodiesterase activity. The soluble enzyme(s) hydrolyzed both cyclic AMP and cyclic GMP, with apparent K m values of 125 and 30 μ m, respectively. Soluble cyclic AMP phosphodiesterase showed marked inhibition by the calcium chelator, ethylene glycol bis(β-aminoethyl ether)- N,N′-tetraacetic acid (EGTA), and the anticalmodulin drugs, chlorpromazine, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), and calmidazolium. No alteration in soluble cyclic GMP phosphodiesterase activity was observed when cyclic AMP was added to the assay. Resolution of the soluble enzymatic activity by DEAE-cellulose chromatography in the presence of calcium showed two peaks of phosphodiesterase activity. Further purification of one of these peaks on DEAE-cellulose in the presence of EGTA yielded a phosphodiesterase activity peak that was stimulated fivefold by calmodulin. The particulate form of the enzyme hydrolyzed both cyclic AMP and cyclic GMP; the apparent K m values for these substrates were similar (90 and 100 μ m, respectively). Hydrolysis of cyclic GMP by the particulate enzyme was inhibited by cyclic AMP in a concentration-dependent manner with an apparent half-maximal inhibitory concentration of 100 μ m. The particulate form of phosphodiesterase was not inhibited by EGTA or anticalmodulin drugs.