A particulate guanylate cyclase (EC 4.6.1.2) from growing yeast cells (Saccharomyces cerevisiae)

The detection of cGMP in yeast (Eckstein 1988), but lacking hints at guanylate cyclase from sequencing of the yeast genome, raised questions about existence, isoform, and regulation of guanylate cyclase from this organism. We found a particulate guanylate cyclase activity in yeast extracts, exhibiting properties of an integral membrane protein. Characteristics are: pH-optimum at pH 6.8, temperature-optimum around 60 degrees C, only slight stimulation by Mn2+. Sigmoidal enzyme kinetics indicate allosteric regulation, ATP and Ca2+ act as negative allosteric effectors. The enzyme activity is increased by yeast alpha-1 mating factor, and by sodium nitrite, thus showing properties of particulate as well as of soluble isoforms from other eukaryotes. The activation by alpha-1 mating factor suggests receptor functions, and a role in ascospore conjugation.