title: Catalase-free photosystem II: the O2-evolving complex does not dismutate hydrogen peroxide.
abstract: A photosystem II (PSII) membrane-associated heme catalase has been identified as a major source of the dark H2O2-dismutation reaction in PSII membrane samples [Sheptovitsky, Y. G., and Brudvig, G. W. (1996) Biochemistry 35, 16255-16263]. Based on this finding, a catalase-free PSII membrane sample was prepared by using mild heat treatment to deplete most of the PSII membrane-associated heme catalase followed by inhibition of the residual catalase with 50 mM 3-amino-1,2,4-triazole, a specific heme catalase inhibitor that binds covalently to compound I. After these treatments, the PSII membrane sample exhibited only 0.02% of the original H2O2-dismutation activity when assayed in the presence of 20 mM 3-amino-1,2,4-triazole. This small residual H2O2-dismutation activity is attributed to adventitious metal ions or the non-heme iron in PSII because the activity was still present in a Mn-depleted PSII sample but was completely suppressed by adding 5 mM ferricyanide to the assay buffer; the effect of ferricyanide is attributed to oxidation of H2O2-dismutating cations. Although the H2O2-dismutation activity was completely eliminated by these treatments, the light-induced O2-evolution activity was retained. A single saturating flash given to catalase-free PSII membranes did not induce any H2O2-dismutation activity. These results demonstrate that the S1/S-1 and S2/S0 cycles of the O2-evolving complex of PSII do not occur in the presence of H2O2, as proposed by Velthuys, B., and Kok, B. [(1978) Biochim. Biophys. Acta 502, 211-221]. The light-induced O2-evolution activity in catalase-free PSII was found to be irreversibly impaired by micromolar concentrations of H2O2. Thus, it is possible that the PSII membrane-associated heme catalase plays an important role in protection of the O2-evolving complex from damage by H2O2.
authors.affiliation: Department of Chemistry, Yale University, New Haven, Connecticut 06520-8107, USA.
authors.forename: Y G
authors.initials: YG
authors.lastname: Sheptovitsky
authors.forename: G W
authors.initials: GW
authors.lastname: Brudvig
mesh_terms: D020642:Acatalasia; D002374:Catalase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003624:Darkness; D006861:Hydrogen Peroxide / Q000378:metabolism*; D008027:Light; D008956:Models, Chemical; D010100:Oxygen / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000302:isolation & purification / Q000378:metabolism* / Q000528:radiation effects; D045332:Photosystem II Protein Complex; D018724:Spinacia oleracea
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D006861:Hydrogen Peroxide; D002374:Catalase; D010100:Oxygen