Physical Studies of α-βγ Subunit Interactions of the Rod Outer Segment G Protein, Gt: Effects of Monoclonal Antibody Binding

  • M. R. Mazzoni
  • H. E. Hamm
Part of the NATO ASI Series book series (NSSA, volume 194)


A guanine nucleotide-binding regulatory protein, called transducin or G t couples light-activated rhodopsin with the cGMP phosphodiesterase (Hurley, 1980). Like all G proteins, transducin is a heterotrimer composed of two distinct subunits: αt (39 kDa) and βγtt: 36 kDa, γt: 8 kDa). The αt subunit binds GDP and GTP (Fung and Stryer, 1980), and in its GTP-bound form activates the cGMP phosphodiesterase (Fung et al., 1981). The activation is terminated when the bound GTP is hydrolyzed to GDP by an intrinsic GTPase activity (Wheeler and Bitensky, 1977, Fung et al., 1981). Although the βγt subunit does not directly participate in either GTP hydrolysis or phosphodiesterase activation, its presence is important for effective binding of αt to photolyzed rhodopsin and GTP-GDP exchange (Fung, 1983). Transducin binds tightly to photolyzed rhodopsin in intact rod outer segment membranes (Kühn, 1980). It also binds selectively to unphotolyzed rhodopsin in rod outer segment membranes (Hamm et al., 1987) and in reconstituted phospholipid vesicles (Fung, 1983).


Antigenic Site Sucrose Density Gradient Sedimentation Coefficient Sucrose Density Gradient Centrifugation High Density Fraction 
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Copyright information

© Plenum Press, New York 1990

Authors and Affiliations

  • M. R. Mazzoni
    • 1
  • H. E. Hamm
    • 1
  1. 1.Department of Physiology and BiophysicsUniversity of Illinois, College of MedicineChicagoUSA

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