title: Preactivation as a determinant for the size of thyroid adenylate cyclase.
abstract: The molecular weight of NaF-activated, Triton N-101-solubilized adenylate cyclase from bovine thyroid membranes has been measured by a combination of sucrose density centrifugation and gel exclusion chromatography. The physical parameters are: sedimentation coefficient, 6.6 S; Stokes radium 41 A; partial specific volume, 0.75 ml/g; molecular weight, 119,000. This is in contrast to the molecular weight (159,000) of the enzyme from the same source activated with guanosine 5'-(beta, gamma-imido)triphosphate. Both soluble adenylate cyclase enzymes are subject to cholera toxin-mediated ADP-ribosylation. This implies that the diminished molecular weight of the NaF-activated solubilized adenylate cyclase is a consequence of one of the following: loss of a GTP-binding protein and labeling of some other protein in the cyclase complex; loss of another protein not subject to cholera toxin labeling; or that two GTP-binding proteins normally reside within the catalytic complex and upon NaF activation one is lost.
mesh_terms: D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D002462:Cell Membrane / Q000201:enzymology; D002772:Cholera Toxin / Q000494:pharmacology; D004789:Enzyme Activation; D005459:Fluorides / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000378:metabolism; D008345:Manganese / Q000494:pharmacology; D008970:Molecular Weight; D013961:Thyroid Gland / Q000201:enzymology*
chemical_list: D000246:Adenosine Diphosphate Ribose; D008345:Manganese; D006160:Guanosine Triphosphate; D002772:Cholera Toxin; D000262:Adenylyl Cyclases; D005459:Fluorides