IDENTIFICATION OF GUANINE-NUCLEOTIDE-BINDING REGULATORY PROTEINS IN BOVINE TRACHEAL SMOOTH-MUSCLE

The identity of G-proteins in airway smooth muscle is not well elucida ted. In the present study, by immunoblotting using AS/7 antibody speci fic for G(i alpha-1/2), EC/2 antibody specific for G(i alpha-3) and RM /1 antibody specific for G(s alpha), we identified, respectively, Mr 3 9, 41, 46 and 52 KDa, Mr 41 and 43 KDa, and Mr 43 and 46 KDa polypepti des of conventional (heterotrimeric) G-proteins in purified membranes of bovine tracheal smooth muscle. The identity of the Mr 41, 43 and 52 KDa G(i alpha), and the Mr 43 and 46 (s alpha) was also confirmed by ADP-ribosylation with pertussis and cholera toxins, respectively. In a ddition, the common antibody (AG/1) for both G(i alpha) and G(s alpha) revealed the presence of all the above polypeptides, except the Mr 52 KDa band. By nitrocellulose blot overlay with [S-35]GTP gamma S, we a lso detected seven low molecular weight GTP-binding proteins of Mr 18- 30 KDa in the bovine tracheal smooth muscle. Photoaffinity crosslinkin g of [alpha-P-32]GTP demonstrated the presence of high molecular GTP-b inding proteins of Mr 55, 75 and 110 KDa. It is concluded that plasma membranes of bovine tracheal smooth muscle contain various types of co nventional, low molecular weight and high molecular weight G-proteins. This warrantes further attention to elucidate the functional roles of G-proteins in airway smooth muscle.