Jj. Abramson et al., o-phthalaldehyde activates the Ca2+ release mechanism from skeletal musclesarcoplasmic reticulum, ARCH BIOCH, 391(2), 2001, pp. 235-244
omicron -Phthalaldehyde (OPA) is a bifunctional reagent that forms an isoin
dole derivative by reacting with cysteine and lysine residues separated by
approximately 0.3 nm. OPA inhibits sarcoplasmic reticulum (SR) Ca2+-ATPase
activity at low micromolar concentrations and induces Ca2+ release from act
ively loaded SR vesicles by activating the ryanodine receptor from fast twi
tch skeletal muscle. Both ryanodine binding and single-channel activity sho
w a biphasic concentration dependence, At low OPA concentrations (< 100 muM
), ryanodine binding and single channel activity are stimulated, while at h
igher concentrations, a time-dependent sequential activation and inhibition
of receptor binding is observed. Activation is characterized by a Ca2+-ind
ependent increase in maximal receptor occupancy, Data are presented to supp
ort a model in which Ca2+ channel and ryanodine binding activity are enhanc
ed due to an intramolecular cross-linking of nearby lysine and nonhyperreac
tive cysteine residues. OPA complexation with endogenous lysine residue(s)
is critical for receptor activation. (C) 2001 Academic Press.