Distinct pH Modulation for Dual Function of Gαh (Transglutaminase II)

• Published in: Journal of biochemistry (Tokyo) 2005-03, Vol.137 (3), p.407-413
• Main Authors: Chae, Kyu Young, Kim, Jin-Hee, Park, Woo-Jae, Kim, Yang-Gyun, Yun, Hye-Young, Kwon, Nyoun Soo, Im, Mie-Jae, Baek, Kwang Jin
• Format: Article
• Language: English
• Subjects: G-protein; GTPase; transglutaminase; α1-adrenoceptor
• ISSN: 0021-924X
• DOI: 10.1093/jb/mvi051

Gαh, also known as transglutaminase II, has GTPase as well as transglutaminase activities. To better understand the factors affecting these dual enzymatic activities, we examined the optimal pH (at 25°C) and thermal stability (at 37°C) of the activities using membranous Gαh from mouse heart. The optimum pH for the GTPase activity of Gαh is ~7.0. As well, the GTP binding activity of Gαh is more thermostable at pH 7.0 than that at pH 9.0. Consistent with these observations on the GTPase function of Gαh, both the phospholipase C-δ1 activity and the yield of co-immunoprecipitation of Gαh-coupled phospholipase C-δ1 in α1-adrenoceptor/Gαh/phospholipase C-δ1 complex preparations were enhanced by incubation with an α1-agonist, phenylephrine, at pH 7.0. On the other hand, the transglutaminase activity of Gαh is higher in the basic pH range with an optimum activity at pH ~9.0. Also, the transglutaminase activity of Gαh is more thermostable at pH 9.0 than that at pH 7.0. These results indicate not only pH as a modulator for the dual functions of Gαh, but also provide direct evidence for the involvement of pH in the Gαh-mediated α1-adrenoceptor signaling system in vitro.