Independent cAMP and cGMP phosphodiesterases in Blastocladiella emersonii

Abstract

CAMP’ and cGMP’ are now recognized as key intracellular regulators in several biological functions, including growth and morphogenesis [ 1,2] . CAMP levels are low during logarithmic growth but rise when contact inhibited cells reach confluency and stop growing [3,4]. The other naturally occurring cyclic nucleotide, cGMP, might also be involved in cell growth regulation, and evidence for an opposing influence of this nucleotide to CAMP, in at least certain stages of growth, has recently been uncovered [5,6]. The intracellular levels of cyclic nucleotides are controlled by synthesis via adenylate or guanylate cyclases, and by degradation via cyclic nucleotide phosphodiesterases. In many cell types there are at least two and perhaps more forms of phosphodiesterases [7]. Chicken embryonic fibroblasts possess CAMP and cGMP phosphodiesterase activities under separate genetic control [8]. The presence of a CAMP phosphodiesterase activity exhibiting a cyclic fluctuation throughout the life cycle has been demonstrated in Blastocladiella emersonii [9]. Variations in the size of the intracellular pools of CAMP and cGMP during the life cycle of this fungus have been reported; however, a cGMP phosphodiesterase activity was not found [lo] . The present