title: Magnesium binding to DM-nitrophen and its effect on the photorelease of calcium.
abstract: The effect of Mg(2+) on the process of Ca(2+) release from the caged Ca(2+) compound DM-nitrophen (NP) was studied in vitro by steady light UV photolysis of NP in the presence of Ca(2+) and Mg(2+). Ca(2+) release during photolysis and its relaxation/recovery after photolysis were monitored with the Ca(2+)-sensitive dye fura-2. Mg(2+) speeds the photorelease of Ca(2+) during photolysis and slows the relaxation of Ca(2+) to new steady-state levels after photolysis. Within the context of a model describing NP photolysis, we determined the on and off rates of Mg(2+) binding to unphotolyzed NP (k(on) = 6.0 x 10(4) M(-1) s(-1); k(off) = 1.5 x 10(-1) s(-1)). Furthermore, to fully account for the slow postphotolysis kinetics of Ca(2+) in the presence of Mg(2+) we were forced to add an additional photoproduct to the standard model of NP photolysis. The additional photoproduct is calculated to have a Ca(2+) affinity of 13.3 microM and is hypothesized to be produced by the photolysis of free or Mg(2+)-bound NP; photolysis of Ca(2+)-bound NP produces the previously documented 3 mM Ca(2+) affinity photoproduct.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA.
authors.forename: R K
authors.initials: RK
authors.lastname: Ayer
authors.forename: R S
authors.initials: RS
authors.lastname: Zucker
mesh_terms: D000085:Acetates / Q000378:metabolism* / Q000528:radiation effects; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000378:metabolism / Q000528:radiation effects; D005029:Ethylenediamines / Q000378:metabolism* / Q000528:radiation effects; D005456:Fluorescent Dyes; D016257:Fura-2; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism*; D008954:Models, Biological; D010777:Photochemistry; D010782:Photolysis; D014466:Ultraviolet Rays
chemical_list: D000085:Acetates; D002614:Chelating Agents; D005029:Ethylenediamines; D005456:Fluorescent Dyes; C057014:DM-nitrophen; D008274:Magnesium; D002118:Calcium; D016257:Fura-2