The 52 kDa Adp-Ribosylated Protein in the Rat Heart Plasma Membrane: Is It Gsa?
G proteins1 are a family of heterotrimeric molecules that are implicated in a variety of signal transduction processes (for review see 1). ADP-ribosylation is a covalent modification which transfers the ADP-ribose moiety of NAD to cellular acceptor proteins. Several bacterial toxins posses this ADP-ribosyltransferase activity and modify several G proteins. For example, cholera toxin can ADP-ribosylate the α subunits of the G proteins Gs and transducin (1). These toxins may mimic endogenous processes and G proteins may be endogenously ADP-ribosylated. Indeed several authors have demonstrated that Gsα can be ADP-ribosylated by endogenous ADP-ribosyltransferases (2-6). In liver membranes, a 55 kDa protein which was speculated to be Gsα is ADP-ribosylated in both the absence and presence of cholera toxin. In the presence of isoproterenol ADP-ribosylation of this protein is increased (6). In NG108-15 hybrid cells (5) and in platelets (4) ADP-ribosylation of Gsα has been implicated in heterologous desensitization to prostacyclins. Recently, it was also shown that in canine sarcolemma, adenylyl cyclase might be regulated by endogenous, reversible ADP-ribosylation of Gsα (7).
KeywordsCholera Toxin Plasma Membrane Fraction Signal Transduction Process Guanine Nucleotide Binding Protein Liver Membrane
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