title: Ca2+: a stabilizing component of the transglutaminase activity of Galphah (transglutaminase II).
abstract: Galphah (transglutaminase type II; tissue transglutaminase) is a bifunctional enzyme with transglutaminase (TGase) and guanosine triphosphatase (GTPase) activities. The GTPase function of Galphah is involved in hormonal signaling and cell growth while the TGase function plays an important role in apoptosis and in cross-linking extracellular and intracellular proteins. To analyze the regulation of these dual enzymatic activities we examined their calcium-dependence and thermal stability in enzymes from several cardiac sources (mouse heart, and normal, ischemic and dilated cardiomyopathic human hearts). The GTP binding activity of Galphah was markedly inhibited by Ca2+ whereas the TGase activity was strongly stimulated, suggesting that Ca2+ acts as a regulator, switching Galphah from a GTPase to a TGase. The TGase function of Galphah of both mouse and human hearts was more thermostable in the presence of Ca2+.
authors.affiliation: Department of Biochemistry, College of Medicine, Chung-Ang University, Seoul 156-756, Korea.
authors.forename: Sang Cheol
authors.initials: SC
authors.lastname: Lee
authors.forename: Jin Hee
authors.initials: JH
authors.lastname: Kim
authors.forename: Eon Sub
authors.initials: ES
authors.lastname: Park
authors.forename: Dae Kyong
authors.initials: DK
authors.lastname: Kim
authors.forename: Yang-Gyun
authors.initials: YG
authors.lastname: Kim
authors.forename: Hye-Young
authors.initials: HY
authors.lastname: Yun
authors.forename: Nyoun Soo
authors.initials: NS
authors.lastname: Kwon
authors.forename: Mie-Jae
authors.initials: MJ
authors.lastname: Im
authors.forename: Kwang Jin
authors.initials: KJ
authors.lastname: Baek
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004795:Enzyme Stability / Q000502:physiology; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006358:Hot Temperature; D006801:Humans; D051379:Mice; D009206:Myocardium / Q000201:enzymology; D000091345:Protein Glutamine gamma Glutamyltransferase 2; D013997:Time Factors; D011503:Transglutaminases / Q000378:metabolism*
chemical_list: D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D002118:Calcium