IDENTIFICATION OF A DISTINCT MOLECULAR-MASS G-ALPHA(H) (TRANSGLUTAMINASE-II) COUPLED TO ALPHA(1)-ADRENOCEPTOR IN MOUSE HEART

Our previous studies on alpha(1)-adrenoceptor signaling suggested that G alpha(h) family is a signal mediator in different species. To eluci date the species-specificity of G alpha(h) family in molecular mass, w e used the solubilized membranes from mouse heart and the ternary comp lex preparations containing alpha(1)-agonist/receptor/G-protein. Bindi ng of [S-35]GTP gamma S and the intensity of the [alpha-P-32]GTP photo affinity labeled protein resulting from activation of the alpha(1)-adr enoceptor were significantly attenuated by the antagonist, phentolamin e. The molecular mass of the specific GTP-binding protein was similar to 72-kDa; homologous with G alpha(h) (transglutaminase II) family. Fu rthermore, immunological cross-reactivity of ternary complex from mous e heart and purified G alpha(h) from rat, guinea pig, and bovine using anti-G alpha(h7) antibody showed that their molecular masses were dis tinctly different and similar to 72-kDa G alpha(h) from mouse heart wa s the lowest molecular mass. Consistent with these observations, in co -immunoprecipitation and co-immunoadsorption of the alpha(1)-adrenocep tor in the ternary complex preparation by anti-G alpha(h7) antibody, t he G alpha(h) family protein tightly coupled to alpha(1)-adrenoceptor. These results demonstrate the species-specificity of G alpha(h) famil y in molecular mass, especially the lowest molecular mass in mouse.