Removal of Mn from spinach chloroplasts by sodium cyanide and the binding of Mn2+ to Mn-depleted chloroplasts.
Manganese and copper were released from spinach chloroplasts by NaCN-treatment, though iron was not affected. The Hill reaction activity was also inhibited by this treatment, but was partially recovered by the addition of either Mn2+ or Cu2+, but not of Fe3+. The interaction of Mn2+ with manganese-depleted chloroplasts by NaCN-treatment was studied using 54Mn2+. A Scatchard plot shows the high and low affinity binding sites of Mn2+ on NaCN-treated chloroplast membrane; high affinity binding being specific for NaCN-treated chloroplast with a binding constant, KH, of 1.9 X 10(5) M-1, and a maximum binding number, NH, of 0.0016 g-atom per mole of chlorophyll. The low binding site was also found on untreated chloroplasts; its binding constant, KL, being 1.2 X 10(4) M-1, and its maximum binding number, NL, of 0.0112 g-atom per mole oc chlorophyll at pH 8.2 NH was proportional to the degree of the removal of Mn by NaCN-treatment and was constant at pH 4--9. NL markedly increased at a high pH with a midpoint of pH 7.9 indicating the exposure of a new, similar binding site. Light illumination partially inhibited the binding of Mn2+. Within 1 min in the dark the binding reaction reached equilibrium in the absence of pyrophosphate, however, 20 min were required to transform into pyrophosphate-resistant form. The pH dependence of the binding of Mn2+ with pKa 7.2 and the ineffectiveness of p-chloromercuribenzoate suggest the possible ligand of Mn2+ is the imidazole nitrogen of the histidine residue.
D015086:2,6-Dichloroindophenol / Q000378:metabolism; D001665:Binding Sites; D001667:Binding, Competitive; D002499:Centrifugation, Density Gradient; D002729:Chloromercuribenzoates / Q000494:pharmacology; D002736:Chloroplasts / Q000187:drug effects / Q000378:metabolism*; D003300:Copper / Q000378:metabolism / Q000494:pharmacology; D003486:Cyanides / Q000494:pharmacology*; D011756:Diphosphates / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000494:pharmacology; D007700:Kinetics; D008345:Manganese / Q000378:metabolism*; D010944:Plants
D002729:Chloromercuribenzoates; D003486:Cyanides; D011756:Diphosphates; D008345:Manganese; D003300:Copper; D015086:2,6-Dichloroindophenol; D007501:Iron