Distinct pH modulation for dual function of G alpha(h) (transglutaminase II)

초록

G alpha(h), 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 degrees C) and thermal stability (at 37 degrees C) of the activities using membranous G alpha(h) from mouse heart. The optimum pH for the GTPase activity of G alpha(h) is similar to 7.0. As well, the GTP binding activity of G alpha(h) is more thermostable at pH 7.0 than that at pH 9.0. Consistent with these observations on the GTPase function of G alpha(h), both the phospholipase C-delta 1 activity and the yield of co-immunoprecipitation of G alpha(h)-coupled phospholipase C-delta 1 in alpha(1)-adrenoceptor/G alpha(h)/phospholipase C-delta 1 complex preparations were enhanced by incubation with an alpha(1)-agonist, phenylephrine, at pH 7.0. On the other hand, the transglutaminase activity of G alpha(h) is higher in the basic pH range with an optimum activity at pH similar to 9.0. Also, the transglutaminase activity of G alpha(h) 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 G alpha(h), but also provide direct evidence for the involvement of pH in the G alpha(h)-mediated alpha(1)-adrenoceptor signaling system in vitro.

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