Effect of metal bound to the substrate site on calcium release from the phosphoenzyme intermediate of sarcoplasmic reticulum ATPase.

摘要: The ADP-sensitive phosphoenzyme intermediate (E1P) of sarcoplasmic reticulum ATPase was formed using CaATP as a substrate and release its bound calcium investigated. Our previous study (Shigekawa, M., Wakabayashi, S., Nakamura, H. (1983) J. Biol. Chem. 258, 14157-14161) indicated that 1 mol E1P has 3 high affinity binding sites for Ca2+, which two are transport whereas the remainder is presumably nucleotide site. to site readily replaced by other divalent cations or lanthanide ions. These ions induced pronounced change in rate Ca2+ from on same phosphoenzyme. In E1P, whose had been deprived metal, fast. It similar normal occupied either Mg2+, it accelerated increasing pH ATP inhibited markedly treatment enzyme with phospholipase C. Release rendered metal-free, increased fluorescence intensity enzyme-bound 2'(3')-O-(2,4,6-trinitrophenyl)adenosine 5'-triphosphate, decayed rapidly upon addition Mg2+ plus K+. This result suggests active resultant cation-free conformation ADP-insensitive phosphoenzyme, E2P. data suggest basic mechanism may be whether not metal at site, although this affects extensively.