Characterization of inhibitory effects of NH 2 OH and its N-methyl derivatives on the O 2 -evolving complex of Photosystem II

Inorganic cofactors (Mn, Ca 2+ and Cl - ) are essential for oxidation of H 2 O to O 2 by Photosystem II. The Mn reductants NH 2 OH and its N-methyl derivatives have been employed as probes to further examine the interactions between these species and Mn at the active site of H 2 O oxidation. Results of these studies show that the size of a hydroxylamine derivative regulates its ability to inactivate O 2 evolution activity, and that this size-dependent inhibition behavior arises from the protein structure of Photosystem II. A set of anions (Cl - , F - and SO 4 2- ) is able to slow NH 2 OH and CH 3 NHOH inactivation of intact Photosystem II membranes by exerting a stabilizing influence on the extrinsic 23 and 17 kDa polypeptides. In contrast to this non-specific anion effect, only Cl - is capable of attenuating CH 3 NHOH and (CH 3 ) 2 NOH inhibition in salt-washed preparations lacking the 23 and 17 kDa polypeptides. However, Cl - fails to protect against NH 2 OH inhibition in salt-washed membranes. These results indicate that the attack by NH 2 OH and its N-methyl derivatives on Mn occurs at different sites in the O 2 -evolving complex. The small reductant NH 2 OH acts at a Cl - -insensitive site whereas the inhibitions by CH 3 NHOH and (CH 3 ) 2 NOH involve a site that is Cl - sensitive. These findings are consistent with earlier studies showing that the size of primary amines controls the Cl - sensitivity of their binding to Mn in the O 2 -evolving complex.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43537/1/11120_2004_Article_BF00046773.pd

In Vivo Serial MR Imaging of Magnetically Labeled Endothelial Progenitor Cells Homing to the Endothelium Injured Artery in Mice

Background: Emerging evidence of histopathological analyses suggests that endothelial progenitor cells (EPCs) play an important role in vascular diseases. Neointimal hyperplasia can be reduced by intravenous transfusion of EPCs after vascular injury in mice. Therefore, it would be advantageous to develop an in vivo technique that can explore the temporal and spatial migration of EPCs homing to the damaged endothelium noninvasively. Methodology/Principal Findings: The left carotid common artery (LCCA) was injured by removal of endothelium with a flexible wire in Kunming mice. EPCs were collected by in vitro culture of spleen-derived mouse mononuclear cells (MNCs). EPCs labeling was carried out in vitro using Fe2O3-poly-L-lysine (Fe2O3-PLL). In vivo serial MR imaging was performed to follow-up the injured artery at different time points after intravenous transfusion of EPCs. Vessel wall areas of injured artery were computed on T2WI. Larger MR signal voids of vessel wall on T2WI was revealed in all 6 mice of the labeled EPC transfusion group 15 days after LCCA injury, and it was found only in 1 mouse in the unlabeled EPC transfusion group (p = 0.015). Quantitative analyses of vessel wall areas on T2WI showed that the vessel wall areas of labeled EPC transfusion group were less than those of unlabeled EPC transfusion group and control group fifteen days after artery injury (p,0.05). Histopathological analyses confirmed accumulation and distribution of transfused EPCs at the injury site of LCCA. Conclusions/Significance: These data indicate that MR imaging might be used as an in vivo method for the tracking of EPC

Mn 2+ reduces Y z + in manganese-depleted Photosystem II preparations

Manganese in the oxygen-evolving complex is a physiological electron donor to Photosystem II. PS II depleted of manganese may oxidize exogenous reductants including benzidine and Mn 2+ . Using flash photolysis with electron spin resonance detection, we examined the room-temperature reaction kinetics of these reductants with Y z + , the tyrosine radical formed in PS II membranes under illumination. Kinetics were measured with membranes that did or did not contain the 33 kDa extrinsic polypeptide of PS II, whose presence had no effect on the reaction kinetics with either reductant. The rate of Y z + reduction by benzidine was a linear function of benzidine concentration. The rate of Y z + reduction by Mn 2+ at pH 6 increased linearly at low Mn 2+ concentrations and reached a maximum at the Mn 2+ concentrations equal to several times the reaction center concentration. The rate was inhibited by K + , Ca 2+ and Mg 2+ . These data are described by a model in which negative charge on the membrane causes a local increase in the cation concentration. The rate of Y z + reduction at pH 7.5 was biphasic with a fast 400 μs phase that suggests binding of Mn 2+ near Y z + at a site that may be one of the native manganese binding sites.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43534/1/11120_2004_Article_BF00048306.pd