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 g uanylate cyclase from sequencing of the yeast genome, raised questions about existence, isoform, and regulation of guanylate cyclase from th is organism. We found a particulate guanylate cyclase activity in yeas t extracts, exhibiting properties of an integral membrane protein. Cha racteristics 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 allosteri c effecters. 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 b y alpha-1 mating factor suggests receptor functions, and a role in asc ospore conjugation.