TY - JOUR
T1 - Interactions Between Diphenylcarbazide, Zinc, Cobalt, and Manganese on the Oxidizing Side of Photosystem II
AU - Ghirardi, Maria L.
AU - Lutton, Thomas W.
AU - Seibert, Michael
PY - 1996
Y1 - 1996
N2 - The inhibition of DPC-mediated DCIP photoreduction by exogenous MnCl2 in Tris-treated photosystem II (PSII) membrane fragments has been used to probe for amino acids on the PSII reaction center proteins, including D1His337, that provide ligands for binding manganese [Preston, C., and Seibert, M. (1990) in Current Research in Photosynthesis (Baltscheffsky, M., Ed.) Vol. 1, pp 925-928, Kluwer Academic Publishers, Dordrecht, The Netherlands: Preston, C., and Seibert, M. (1991) Biochemistry 30, 9615-9624 and 9625-9633]. At a concentration of 200 μM, DPC is photooxidized at both a high-affinity and a low-affinity site in PSII at approximately the same initial ate. Addition of 10 μM MnCl2 noncompetitively inhibits DPC photooxidation at the high- affinity site, with a K1 of 1.5 μM, causing a decrease of about 50% in the overall DCIP photoreduction rate. The high-affinity site for Mn binding was deconvoluted into four independent components. In earlier work, the inhibition was attributed to the tight association of either Mn2+ or Mn3+ with the PSII membrane. We report here that inhibition of DPC photooxidation may involve two different types of high-affinity, Mn-binding components: (a) one that is specific for Mn, and (b) others that bind Mn, but may also bind additional divalent cations, such as Zn and Co, that are not photooxidized by PSII. These conclusions are based on the observations that (a) DPC photooxidation can be inhibited by Zn2+ and Co2+; (b) Zn2+ and Co2+ interact with Mn2+ in a nonmutually exclusive manner, suggesting that they may share some binding components with Mn2+ in a nonmutually exclusive manner, suggesting that they may share some binding components with Mn2+; (c) high-affinity Mn2+ (but not Zn2+ or Co2+) inhibition of DPC photooxidation is accompanied by nondecaying fluorescence emission, following a single saturating flash, indicating efficient electron donation by Mn2+ to Y(Z); (d) Mn2+ photooxidation in the presence of DPC is not inhibited by Zn2+ or Co2+; and (e) kinetic modeling of the interaction between high- affinity Mn2+ and DPC in PSII indicates inhibition of steady-slate Mn2+ photooxidation by DPC, but allows for a single photooxidation of Mn2+. We conclude that Mn inhibition of DPC photooxidation can be used to identify Mn- binding sites of physiological importance, and suggest that the Mn-specific component of the high-affinity, Mn-binding site involves the ligand to the first Mn bound during photoactivation (i.e., Asp170 on D1, as found by other investigators).
AB - The inhibition of DPC-mediated DCIP photoreduction by exogenous MnCl2 in Tris-treated photosystem II (PSII) membrane fragments has been used to probe for amino acids on the PSII reaction center proteins, including D1His337, that provide ligands for binding manganese [Preston, C., and Seibert, M. (1990) in Current Research in Photosynthesis (Baltscheffsky, M., Ed.) Vol. 1, pp 925-928, Kluwer Academic Publishers, Dordrecht, The Netherlands: Preston, C., and Seibert, M. (1991) Biochemistry 30, 9615-9624 and 9625-9633]. At a concentration of 200 μM, DPC is photooxidized at both a high-affinity and a low-affinity site in PSII at approximately the same initial ate. Addition of 10 μM MnCl2 noncompetitively inhibits DPC photooxidation at the high- affinity site, with a K1 of 1.5 μM, causing a decrease of about 50% in the overall DCIP photoreduction rate. The high-affinity site for Mn binding was deconvoluted into four independent components. In earlier work, the inhibition was attributed to the tight association of either Mn2+ or Mn3+ with the PSII membrane. We report here that inhibition of DPC photooxidation may involve two different types of high-affinity, Mn-binding components: (a) one that is specific for Mn, and (b) others that bind Mn, but may also bind additional divalent cations, such as Zn and Co, that are not photooxidized by PSII. These conclusions are based on the observations that (a) DPC photooxidation can be inhibited by Zn2+ and Co2+; (b) Zn2+ and Co2+ interact with Mn2+ in a nonmutually exclusive manner, suggesting that they may share some binding components with Mn2+ in a nonmutually exclusive manner, suggesting that they may share some binding components with Mn2+; (c) high-affinity Mn2+ (but not Zn2+ or Co2+) inhibition of DPC photooxidation is accompanied by nondecaying fluorescence emission, following a single saturating flash, indicating efficient electron donation by Mn2+ to Y(Z); (d) Mn2+ photooxidation in the presence of DPC is not inhibited by Zn2+ or Co2+; and (e) kinetic modeling of the interaction between high- affinity Mn2+ and DPC in PSII indicates inhibition of steady-slate Mn2+ photooxidation by DPC, but allows for a single photooxidation of Mn2+. We conclude that Mn inhibition of DPC photooxidation can be used to identify Mn- binding sites of physiological importance, and suggest that the Mn-specific component of the high-affinity, Mn-binding site involves the ligand to the first Mn bound during photoactivation (i.e., Asp170 on D1, as found by other investigators).
UR - http://www.scopus.com/inward/record.url?scp=0030047238&partnerID=8YFLogxK
U2 - 10.1021/bi951657d
DO - 10.1021/bi951657d
M3 - Article
C2 - 8639663
AN - SCOPUS:0030047238
SN - 0006-2960
VL - 35
SP - 1820
EP - 1828
JO - Biochemistry
JF - Biochemistry
IS - 6
ER -