[Interaction of ATP with sarcoplasmic reticulum Ca2+-ATPase; effect on the conformational state of the enzyme]

It was studied how temperature influences the NBD-Cl inactivation of sarcoplasmic reticulum Ca2+-ATPase and the protective effect of ATP under conditions preventing ATP hydrolysis. Two types of ATP-binding sites with Kd equal to 30 and 220 microM at 37 degrees C were found. ADP interacts with these sites with the (K'd = 20 and 200 microM). The temperature decrease from 25 degrees to 5 degrees C induces the abrupt increase in the Kd for the low affinity site. The possible reasons for heterogeneity of ATP-binding sites are discussed. The conclusion is made that interaction of monomers in oligomeric complex of Ca2+-ATPase induces heterogeneity of ATP-binding sites.