Ascomycetes Ascomycota GTP-binding proteins Mammalia Saccobolus Saccobolus platensis Vertebrata adenosine triphosphate article ascomycete binding competition cholera toxin dissociation constant guanine nucleotide binding protein guanosine triphosphate immunoblotting membrane binding nonhuman photodifferentiation polyacrylamide gel electrophoresis priority journal protein subunit sulfur 35