Ca2+: a stabilizing component of the transglutaminase activity of Galphah (transglutaminase II).
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+.
Lee
Sang Cheol
SC
Department of Biochemistry, College of Medicine, Chung-Ang University, Seoul 156-756, Korea.
Kim
Jin Hee
JH
Park
Eon Sub
ES
Kim
Dae Kyong
DK
Kim
Yang-Gyun
YG
Yun
Hye-Young
HY
Kwon
Nyoun Soo
NS
Im
Mie-Jae
MJ
Baek
Kwang Jin
KJ
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*
D000091345:Protein Glutamine gamma Glutamyltransferase 2; D011503:Transglutaminases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins; D002118:Calcium