Mn(2+)-activated luminescence of the photoprotein obelin.
The light emission of obelin may be initiated by Mn2+ under alkaline conditions. The luminescence takes place in a pH range from 7 to 12 with a sharp optimum at 11.75. The first-order rate constant for Mn(2+)-activated luminescence decay is more than 9 s-1, while that for Ca(2+)-activated luminescence decay is only 6.9 s-1. The Mn2+ concentration-effect curve for obelin determined with simple dilutions of manganese salt is a sigmoid curve. The slope of the curve is moderately dependent on the pH and was not more than 1 within the pH range tested. The maximal light emission, which is initiated by 3.6 x 10(-5) M Mn2+ at pH 11.75 was about 10% of the maximal Ca(2+)-activated luminescence. Mg2+ ions inhibit the Mn(2+)-activated luminescence of obelin. The addition of OH. and O2- scavengers did not influence the Mn(2+)-activated luminescence, but when singlet oxygen quenchers were added, the Mn(2+)-dependent light emission was inhibited. This suggests that the 1O2 might be formed and itself be responsible for chromophore oxidation attended with light emission. NEM and Na2S2O4 inhibit the Mn(2+)-initiated light emission of obelin completely, showing that endogenous hydroperoxide and SH-group(s) of the photoprotein are essential for both Ca(2+)-activated and Mn(2+)-activated light emission of obelin.
Institute of Biophysics, Russian Academy of Sciences, Siberian Branch, Krasnoyarsk.
E S
ES
Vysotski
C P
CP
Trofimov
V S
VS
Bondaŕ
L A
LA
Frank
S V
SV
Markova
B A
BA
Illarionov
D000331:Aequorin / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D003063:Cnidaria / Q000737:chemistry* / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D016166:Free Radical Scavengers / Q000494:pharmacology; D005609:Free Radicals; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles; D007700:Kinetics; D008027:Light; D008163:Luminescent Measurements; D008164:Luminescent Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D008345:Manganese / Q000378:metabolism* / Q000494:pharmacology; D008956:Models, Chemical; D011719:Pyrazines; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D013885:Thiosulfates / Q000494:pharmacology
D016166:Free Radical Scavengers; D005609:Free Radicals; D007093:Imidazoles; D008164:Luminescent Proteins; D011719:Pyrazines; D011994:Recombinant Proteins; D013439:Sulfhydryl Reagents; D013885:Thiosulfates; C010497:obelin; C017144:coelenterazine; D008345:Manganese; D000331:Aequorin; C017717:sodium thiosulfate