Activation of transglutaminase at calcium levels consistent with a role for this enzyme as a calcium receptor protein.
The sensitivity of tissue transglutaminase to activation by Ca2+ and other cellular factors was investigated using the enzyme purified from rat liver. The inclusion of Mg2+ in the assay system appeared to reduce the Ca2+-requirement of the enzyme when native N,N'-dimethylcasein was used as the protein acceptor substrate. However, when this protein was dephosphorylated, the Ca2+-requirement was unaffected by Mg2+. In addition, using this modified assay, a Km for Ca2+ was calculated to be in the range of 3-4 microM, at least an order of magnitude lower than that obtained with native acceptor substrate. Membrane phospholipids, 1,2-diolein and calmodulin were found not to affect the activation of transglutaminase by Ca2+. The sensitivity of transglutaminase to Ca2+ which we have now demonstrated suggests that this enzyme may directly act as a receptor protein for Ca2+ during stimulus-response coupling mediated by this cation.
Hand
D
D
Bungay
P J
PJ
Elliott
B M
BM
Griffin
M
M
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism* / Q000502:physiology; D002147:Calmodulin / Q000494:pharmacology; D004789:Enzyme Activation; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008274:Magnesium / Q000378:metabolism; D010743:Phospholipids / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011503:Transglutaminases / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology
D002135:Calcium-Binding Proteins; D002147:Calmodulin; D010743:Phospholipids; D011503:Transglutaminases; D008274:Magnesium; D002118:Calcium