Differences in the susceptibility of various cation transport ATPases to vanadate-catalyzed photocleavage.

Illumination of sarcoplasmic reticulum vesicles by ultraviolet light in the presence of 1 mM vanadate causes photocleavage of the Ca(2+)-ATPase into two fragments (Vegh et al. (1990) Biochim. Biophys. Acta 1023, 168-183). In the absence of Ca2+ the photocleavage occurs in the N-terminal half of the molecule near the phosphate acceptor Asp-351. In the presence of 2 mM Ca2+ the photocleavage shifts to the C-terminal half of the ATPase, near the FITC binding site (Lys-515). About half of the Ca(2+)-ATPase was cleaved rapidly, accompanied by nearly complete, irreversible loss of ATPase activity when illuminated in the presence of 2 mM CaCl2; further cleavage of the enzyme was slow and affected primarily the C-terminal fragment produced in the presence of Ca2+. Solubilization of the Ca(2+)-ATPase with C12E8 did not affect the site of photocleavage in either conformation. The vanadate-induced Ca(2+)-ATPase crystals were disrupted during photocleavage, while the binding of anti-ATPase antibodies directed against the phosphorylation site (PR-8) and against the FITC binding region (PR-11) was enhanced. The bovine kidney Na+,K(+)-ATPase was insensitive to photocleavage under conditions where about half the Ca(2+)-ATPase was fragmented. The slight cleavage of the pig gastric H+,K(+)-ATPase after prolonged illumination produced fragments that are distinct from the fragments of the Ca(2+)-ATPase.