| Abstract: | In continuation of our efforts to reconstitute from purified components into lipid vesicles the signal transmission chain from beta 1-adrenoceptors to adenylate cyclase, we now report on the total reconstitution of the hormone-dependent adenylate cyclase. In these reconstitution experiments we have employed the purified adenylate cyclase (C) from bovine brain and rabbit heart, the stimulatory GTP-binding protein (GS) purified from turkey erythrocytes and rabbit liver and the beta 1-adrenoceptor (R) from turkey erythrocytes. Several detergents were compared with respect to their suitability to allow reconstitution of subunits into phospholipid vesicles. While octyl-polyoxyethylene (octyl-POE) was almost as potent as lauroyl-sucrose for preparation of vesicles containing GS.C, the latter detergent was clearly superior for vesicles enabling productive R.GS and R.GS.C coupling. The catalytic subunit from either bovine brain or rabbit heart was equally efficient in reconstitution. However, GS from turkey erythrocytes and rabbit liver revealed significant differences in RGS and RGS.C containing vesicles. While isoproterenol-induced activation of GS by GTP gamma S was first order in both instances, kon with turkey GS was 0.12 min-1, whereas kon with rabbit liver GS was 0.6 min-1. Moreover, GTP gamma S activation of erythrocyte GS was significantly more dependent on the presence of hormone than that of liver GS, confirming observations made on the native membrane-bound system. Compared with stimulation by isoproterenol (GTP gamma S) (4-fold), stimulation by isoproterenol/GTP was modest (1.3- to 1.6-fold).(ABSTRACT TRUNCATED AT 250 WORDS) |
