GUANINE-NUCLEOTIDE BINDING-PROTEINS ACTIVATE ADENYLATE-CYCLASE FROM SEA-URCHIN SPERM

1. Stimulation of adenylate cyclase of sea urchin sperm by neurotransmitters and guanine nucleotide binding protein activators has been investigated. 2. 2. Sea urchin sperm cyclase does not respond to neurotransmitters, including dopamine, which is the most active stimulator of sea urchin egg adenylate cyclase. 3. 3. Unlike mammalian sperm cyclase, the unresponsiveness of the sea urchin sperm enzyme to neurotransmitters cannot be ascribed to a defect of signal transduction. 4. 4. The adenylate cyclase of sea urchin sperm is activated by fluoride, guanine nucleotides and cholera toxin, thus demonstrating the presence of a functioning guanine nucleotide binding protein.