Variations in the levels of cyclic adenosine 3':5'-monophosphate and in the activities of adenylate cyclase and cyclic adenosine 3':5'-monophosphate phosphodiesterase during aerobic morphogenesis of Mucor rouxii

Particulate cell fractions of mycelium of Mucor rouxii contain adenylate cyclase activity which can be partially solubilized by 2% Lubrol PX. The enzyme requires Mn²⁺ and its activity is not modified by NaF or guanosine nucleotides. Mycelial extracts also contain cyclic adenosine 3′:5′-monophosphate phosphodiesterase activity, 60% of which is soluble. This activity shows characteristic low K_m (1 μm) for cyclic AMP and does not hydrolyze cyclic guanosine 3′:5′-monophosphate. It requires Mn²⁺ ions for maximal activity and is not inhibited by methylxanthines or activated by imidazole. Both enzymatic activities vary during the aerobic life cycle of the fungus. The spores have the highest levels of adenylate cyclase and cAMP phosphodiesterase, which decrease during the aerobic development. At the round cell stage, phosphodiesterase activity reaches 40% of the activity of the spores and varies only slightly thereafter. At this stage the specific activity of adenylate cyclase is 25% of the activity of ungerminated spores, and from this stage on, the activity increases up to the end of the logarithmic phase. Intracellular levels of cyclic AMP have been measured during aerobic germination. The variations of the intracellular level are tentatively explained by unequal variations in the activities of adenylate cyclase and cyclic AMP phosphodiesterase. A continuous increase of the extracellular cyclic AMP level during aerobic development has also been found, which cannot be accounted for solely by variations in the cyclase and diesterase activities.