GTP Modulates Calcium Binding and Cation-induced Conformational Changes in Erythrocyte Transglutaminase

Calcium binding to erythrocyte transglutaminase was determined by equilibrium dialysis. Results indicate that 6 ions are bound to the enzyme both in the absence and in the presence of GTP and that the nucleotide reduces the affinity of the enzyme for calcium. Furthermore, I- fluorescence quenching and proteolytic inactivation experiments proved that GTP also alters the conformation of the enzyme. It is thus suggested that multiple mechanisms are involved in the regulation of the enzyme activity by GTP.