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