Changes in cGMP phosphodiesterase levels during growth and differentiation in Blastocladiella EmersonII

Blastocladiella emersonii, a unicellular phycomycete represents a useful organism for experimental studies on the regulatory role of cyclic nucleotides (see ref [ 1 ] for a recent review of the cell cycle). Thus, the levels of CAMP** and cGMP** as well as enzyme activities concerning their metabolism were found to change markedly during the life cycle [2-51. In all living systems so far studied, cGMP is synthesized via guanylate cyclase and hydrolysed via cyclic nucleotide phosphodiesterases. In principle, any alteration in the amount or activity of either of these two enzymes would affect the intracellular cGMP concentration. Thus, it is important to find out if these two enzyme activities are altered as a function of the cell cycle. cGMP levels in B. emersonii are low during the growth stage rising about SO1 OO-fold at a defined stage in its life cycle, during sporulation [3]. We have demonstrated that B. emersonii contains independent specific enzymes involved in the hydrolysis of CAMP and cGMP [6]. The present communication shows that the specific activity of cGMP phosphodiesterase dramatically changes throughout the life cycle of B. emersonii, particularly during germination and sporulation. The results indicate that the observed variation in cGMP levels when cells sporulate [3] reflects the changes in enzymatic activities, mainly in cGMP phosphodiesterase.