Islet-activating protein catalyzes the ADP-ribosylation of transducin at an asparagine residue near the carboxyl terminus of the alpha subunit, distinct from the cholera toxin site.
Identifies asparagine as the specific amino acid residue where islet-activating protein catalyzes ADP-ribosylation on the alpha subunit of transducin.
Islet-activating protein catalyzes the ADP-ribosylation of transducin, a guanine nucleotide-binding regulatory protein that mediates activation of a retinal cyclic GMP-selective phosphodiesterase. Radiolabel from adenylate-32PNAD+ was incorporated specifically into the alpha subunit of purified transducin. Maximal levels of incorporation approximated 0.8 mol of ADP-ribose/mol of transducin. A peptide containing the ADP-ribosyl moiety was purified from a tryptic digest of radiolabeled transducin. This peptide was characterized by chemical and enzymatic procedures and by fast atom bombardment mass spectrometry. The primary structure of this peptide was Glu-Asn-Leu-Lys-Asn(ADP-ribose)-Gly-Leu-Phe. It is probable that the peptide originated from the carboxyl terminus of the alpha subunit and that the ADP-ribosyl moiety is attached by an N-glycosidic linkage to the asparagine residue. Transducin associated with retinal disc membranes is also ADP-ribosylated by cholera toxin. Cholera toxin and islet-activating protein sequentially catalyze the incorporation of 1.9 mol of ADP-ribose/mol of transducin, indicating two distinct sites of ADP-ribosylation within transducin.
Manning et al. (Sun,) reported a other. Islet-activating protein was evaluated on Site of ADP-ribosylation on transducin. Islet-activating protein catalyzes the ADP-ribosylation of transducin at an asparagine residue near the carboxyl terminus of the alpha subunit, distinct from the cholera toxin site.
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