28] Guanylate cyclase from sperm of the sea urchin, Strongylocentrotus purpuratus

Abstract

Publisher Summary Guanylate cyclase activity is measured by estimating radioactive cGMP formation from [3H] GTP. The nature of the phosphate product formed in the reaction has not been reported, although it is known that the α-phosphate of GTP is incorporated into cGMP. Guanylate cyclase is found in much higher activity in sea urchin sperm than in mammalian tissues. The activity in homogenates of sea urchin (Strongylocentrotus purpuratus) sperm ranges from 15 to 60 nmoles of cGMP formed main-1 mg protein-1 at 37°c at pH 7.8 (0.3 mM GTP, 5 mM Mn2+). When measured under similar conditions, the activity in rat lung homogenates ranges from about 0.1 to 0.4 nmole of cGMP formed MaiN-1 mg protein-1. Although guanylate cyclase is largely soluble in most mammalian tissues, the sea urchin sperm enzyme is found in particulate fractions. The enzyme is primarily of flagellar origin and appears to be membrane associated.