Abstract
Gαh (transglutaminase II) is a bifunctional enzyme possessing transglutaminase and GTPase activities. To better understand the factors affecting these two functions of Gαh, we have examined the characteristics of purified Gαh from membrane and cytosol. GTP binding activity of mouse heart Gαh was higher in membrane than that from cytosol. Furthermore, phospholipase C-δ1 (PLC-δ1) activity and coimmunoprecipitation of Gαh-coupled PLC-δ1 in the α1-adrenoceptor–Gαh-PLC-δ1 complex preparations were increased by phenylephrine in the presence of membranous Gαh. On the other hand, transglutaminase activity of cytosolic Gαh was higher than that from membrane Gαh. These results demonstrate that bifunctions of Gαh are regulated by its localization that can reflect the cellular functions of Gαh.
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