The Relationship of G o α Subunit Deamidation to the Tissue Distribution, Nucleotide Binding Properties, and βγ Dimer Interactions of G o α Subunit Isoforms

: The distribution and properties in brain of the α subunits of the major bovine brain G o isoforms, G oA , G oB and G oC , were characterized. The α oA and α oB isoforms arise from alternative splicing of RNAs from a single α o gene, whereas α oC is a deamidated form of α oA . All three G o isoforms purify from brain with different populations of βγ dimers. This variable subunit composition of G o heterotrimers is likely a consequence of their functional differences. This study examined the biochemical properties of the α o isoforms to see if these properties explain the variable βγ composition of their heterotrimers. The brain distribution of α oB differed substantially from that of α oA and α oC , as did its guanine nucleotide binding properties. The unique subunit composition of G oB can be explained by its expression in different brain regions. The α oA and α oC showed slight differences in guanine nucleotide binding properties but no preference for particular βγ dimers when reassociated with a heterogeneous βγ pool. The α oC protein occurred in a constant ratio to α oA throughtout the brain, but was a much larger percent of total brain α o than previously thought, ~35%. These results suggest that α oA is a precursor of αo C and that the association of G o α subunits with different βγ dimers reflects the function of an adaptive, G‐protein signaling mechanism in brain.