Fig. 1.

TGM2-dependent protein incorporation of histamine. (a) Histamine added extracellularly is protein-incorporated. P815 mastocytoma (1 × 10⁶) cells were treated with 1 μCi [³H]-histamine ([³H]-HA), with and without the transglutaminase (TGM) inhibitor cysteamine (CTA), proteins precipitated with PCA, and analyzed by scintillation counting. The [³H]-HA-treatment resulted in radioactive labeling of the protein fraction; transfer of the label was inhibited by CTA. (b) TGM paralogues are expressed in mastocytoma cells. RT-PCR experiments addressing TGM paralogues 1–7 from P815 cDNA. (c) TGM2 transfers histamine to G proteins. 8 μM GST, GST-Cdc42, GST-Gαo1, GST-Gαq or dimethyl caseine (DMC) were incubated for 30 min with 0.3 μM [³H]-HA in combination with TGM1, TGM2 or TGM3. Proteins were precipitated, filtered and analyzed by scintillation counting. (d) Stoichiometry of Gαo1 histaminylation. 1.6 μM GST-Gαo1 and 5 mU TGM2 were incubated for 60 min with differing amounts of [³H]-HA and assayed for radioactivity.