Dehydroascorbate reductase (DHAR) is a key enzyme for glutathione (GSH)-dependent reduction of dehydroascorbate (DHA) to recycled ascorbate (AsA) in plants, and plays a major role against the toxicity of reactive oxygen species (ROS). Previously, we proposed that the increase of AsA regeneration via enhanced DHAR activity modulates the ascorbate-glutathione cycle activity against photooxidative stress in Chlamydomonas reinhardtii. In the present work, we use site-directed mutagenesis and crystal structure analysis to elucidate the molecular basis of how C. reinhardtii DHAR (CrDHAR1) is involved in the detoxification mechanisms. Mutagenesis data show that the D21A, D21N and C22A mutations result in severe loss of the enzyme's function, suggesting crucial roles of Asp-21 and Cys-22 in substrate binding and catalysis. The mutant K11A also exhibits reduced redox activity (∼50%). The crystal structure of apo CrDHAR1 further provides insights into the proposed mechanism centering on the strictly conserved Cys-22, which is suggested to initiate the redox reactions of DHA and GSH. Furthermore, in vitro oxidation of the recombinant CrDHAR1 in the presence of 1 mM H2O2 has minor effects on the Km for the substrates but significantly reduces the kcat. The enzyme's activity and its mRNA abundance in the C. reinhardtii cells are increased by treatment with 0.2-1 mM H2O2 but decreased when H2O2 is ≥ 1.5 mM. The latter decrease is accompanied by oxidative damage and lower AsA concentrations. These biochemical and physiological data provide new insights into the catalytic mechanism of CrDHAR1, which protects the C. reinhardtii cells from oxidative stress-induced toxicity.

Atherosclerosis is the principal cause of mortality in industrialized countries. Its development is influenced by several mediators of which thromboxane A(2) (TXA(2)) and 8-iso-PGF(2α) have recently received a lot of attention. This study aimed to investigate the effect of a dual thromboxane synthase inhibitor and thromboxane receptor antagonist (BM-573) and ASA on lesion formation in apolipoprotein E-deficient mice. The combination of ASA and BM-573 was also studied. Plasma measurements demonstrated that the treatments did not affect body weight or plasma cholesterol levels. BM-573, but not ASA, significantly decreased atherogenic lesions as demonstrated by macroscopic analysis. Both treatments alone inhibited TXB(2) synthesis but only BM-573 and the combination therapy were able to decrease firstly, plasma levels of soluble intracellular adhesion molecule-1 (sICAM-1) and soluble vascular cell adhesion molecule-1 (sVCAM-1) and secondly, the expression of these proteins in the aortic root of Apo E. These results were confirmed in endothelial cell cultures derived from human saphenous vein endothelial cells (HSVECs). In these cells, BM-573 also prevented the increased mRNA expression of ICAM-1 and VCAM-1 induced by U-46619 and 8-iso-PGF(2α). Our results show that a molecule combining receptor antagonism and thromboxane synthase inhibition is more efficient in delaying atherosclerosis in Apo E(-/-) mice than sole inhibition of TXA(2) formation.

Exposure of dark- or ambient visible light-grown broad bean seedlings to low (LL) and high (HL) visible light intensities, UV-A or UV-C, either alone or in combination, induced significant increases in total phenolic compounds as well as in anthocyanins content, throughout the germination period, as compared with the respective levels in control seedlings. In general, as compared with control levels, exposure of both dark- or light-grown broad bean seedlings to LL, HL, UV-A or UV-C, induced significant increases in the contents of non-enzymatic antioxidants (total ascorbate; ASA-DASA and total glutathione; GSSG-GSH) and enzymatic antioxidant activities (superoxide dismutase; SOD, catalase; CAT, ascorbate peroxidase; APO and glutathione reductase; GR). The obtained results are discussed in relation to induced mechanisms of protection and repair from the inevitable exposure to damaging visible light and UV-radiation.

Hydrogen/deuterium exchange (HDX) using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF) is a sensitive, salt-tolerant and high-throughput method useful to probe protein conformation and molecular interactions. However, a drawback of the MALDI HDX technique is that sample preparation methods can typically result in higher levels of artificial deuterium in-exchange and/or hydrogen back- exchange just prior to or during mass analysis; this may impair data reproducibility and impede structural and kinetic data interpretation. While methods to minimize effects of back-exchange during protein analyte deposition on MALDI plates have been reported, this study presents a readily available, highly sensitive protein control set to facilitate rapid MALDI HDX protocol workup. The Ca(2+)-induced solvent accessible surface area (ASA) changes of calmodulin (CaM) and S100 proteins were employed to monitor and optimize HDX protocol efficiency. Under non- stringent room temperature conditions, the Ca(2+)-induced deuterium exchange of CaM, DeltaD(ca2+ -apo), MH(+) shifts -17 to -24 Da, while S100 DeltaD(ca2+ -apo) MH(+) shifts +8 to +12 Da. By comparing the divergent CaM and S100 Ca(2+)-induced deuterium mass shift differences, HDX sample workup and MALDI plate spotting conditions can easily be monitored.