Regulation of cyclic AMP phosphodiesterase from Mucor rouxii by phosphorylation and proteolysis. Interrelationship of the activatable and insensitive forms of the enzyme

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Abstract
DEAE-cellulose chromatography of mycelial extracts of M. rouxii grown to mid-exponential phase resolves 2 types of low-Km cyclic AMP phosphodiesterase (EC 3.1.4.17; PDE): PDE I, highly activatable (4- to 6-fold) by phosphorylation or proteolysis, and PDE II, unresponsive to activation. The enzymic profile of PDE activity obtained from germlings shows only PDE I activity, whereas PDE activity from mycelia grown to stationary phase is eluted from the DEAE-cellulose column at the position of PDE II, and like PDE II is unresponsive to activation. Endogenous proteolysis or controlled trypsin treatment transforms PDE I into PDE II. The insensitive forms of PDE exhibit a slightly smaller sedimentation coefficient than the activatable forms, as judged by sucrose-gradient centrifugation. The basal activity of the highly activatable form of PDE is elevated almost to the value in the presence of trypsin on storage at 4.degree. C in the absence of proteinase inhibitors. Benzamidine, leupeptin, antipain or EGTA [ethyleneglycol bis(ethylamine)tetraacetic acid] prevents the activation produced by storage. PDE I remains strongly activatable by phosphorylation and proteolysis after resolution by polyacrylamide-gel electrophoresis.

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