Abstract
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-32P]NAD+ was incorporated specifically into the α subunit of purified transducin. Maximal levels of incorporation approximated 0.8 mol of ADPribose/mol of transducin. A peptide containing the ADP-ribosyl moiety was purified from a tryptic digest of radiolableled 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 α 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.
Original language | English (US) |
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Pages (from-to) | 749-756 |
Number of pages | 8 |
Journal | Journal of Biological Chemistry |
Volume | 259 |
Issue number | 2 |
State | Published - 1984 |
ASJC Scopus subject areas
- Biochemistry
- Molecular Biology
- Cell Biology