Membranes from bovine brain bind relatively large quantities of guanosine 5'-(3-O-thio)triphosphate (GTPγS) with high affinity. The two proteins responsible for most of this activity were purified; they account for 1.5% of the membrane protein. The two proteins contain α subunits of either 39,000 and 41,000 Da, β subunits of 36,000 or 35,000 Da, and a potential γ subunit (11,000 Da). These structures are the same as a family of proteins that includes transducin and the regulatory proteins, G(S) and G(I), of adenylate cyclase. The 41,000- and 39,000-Da polypeptides can be ADP-ribosylated with islet-activating protein from Bordetella pertussis, bind guanine nucleotides specifically, and migrate through polyacrylamide gels with rates similar to the α subunits of G(I) and transducin, respectively. The 36,000- and 35,000-Da polypeptides are similar to the β subunits of G(I) and G(S). The γ subunit is found whenever β subunits are present. The 41,000- and 39,000-Da polypeptides (with β and γ) are designated, respectively, G(I) and G(O) from brain. The α subunit of G(O) was isolated without the use of ligands known to dissociate other G proteins. G(O)α binds GTPγS reversible in the absence of Mg2+ and is relatively stable in cholate. This isolated α subunit should be of great utility in elucidating the mechanism of action of this family of GTP-binding proteins.
|Original language||English (US)|
|Number of pages||8|
|Journal||Journal of Biological Chemistry|
|State||Published - Dec 1 1984|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology