Hg(2+) reacts with different components of the NADPH : protochlorophyllide oxidoreductase macrodomains.
The molecular background of Hg (2+)-induced inhibition of protochlorophyllide (Pchlide) photoreduction was investigated in homogenates of dark-grown wheat leaves. Our earlier work showed that 15 min incubation with 10 (-2) M Hg (2+) completely inhibits the activity of NADPH : Pchlide oxidoreductase ( ). Detailed analysis of spectra recorded at 10 K indicated the appearance of emission bands at 638 and 650 nm, which are characteristic for NADP (+)-Pchlide complexes. Fluorescence emission spectra recorded with different excitation wavelengths, fluorescence lifetime measurements and the analysis of acetone extractions revealed that Hg (2+) can also react directly with Pchlide, resulting in protopheophorbide formation. At 10 (-3) M Hg (2+), the phototransformation was complete but the blue shift of the chlorophyllide emission band speeded up remarkably. This indicates oxidation of the NADPH molecules that have a structural role in keeping together the etioplast inner membrane components. We suggest a complex model for the Hg (2+) effect: depending on concentration it can react with any components of the NADPH : Pchlide oxidoreductase macrodomains.
Solymosi
K
K
Department of Plant Anatomy, Eötvös University, Budapest, Hungary.
Lenti
K
K
Myśliwa-Kurdziel
B
B
Fidy
J
J
Strzałka
K
K
Böddi
B
B
D004785:Environmental Pollutants / Q000494:pharmacology; D008628:Mercury / Q000494:pharmacology*; D044925:Oxidoreductases Acting on CH-CH Group Donors / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010788:Photosynthesis / Q000187:drug effects / Q000502:physiology*; D018515:Plant Leaves / Q000187:drug effects / Q000201:enzymology*; D014908:Triticum / Q000187:drug effects / Q000201:enzymology*
D004785:Environmental Pollutants; D044925:Oxidoreductases Acting on CH-CH Group Donors; C023886:protochlorophyllide reductase; D008628:Mercury