This is accomplished by the Zeaxanthin Epoxidase (ZEP) which requires O 2 and NADPH as co-substrates 10 and is located at the stromal side of the thylakoid membrane 11. Due to the correlation between qZ and Zx, qZ relaxes slower than qE as Zx needs to be epoxidized back to Vx. While Kress and Jahns 9 argue against a direct involvement of Zx as the quencher itself in qZ, they report a strong correlation between qZ and Zx in plants lacking PsbS as well as in WT plants, when the rapidly relaxing qE component was excluded. More recently, a PsbS-independent NPQ component, qZ, has been identified which kinetically follows the Zx concentration and is relevant during steady state (> 10 min) light conditions 7, 8, 9. While Zx enhances the magnitude of qE, it is not strictly required for it 6. A low pH in the lumen also activates the lumenal xanthophyll cycle (XC) enzyme Violaxanthin De-Epoxidase (VDE) 4, which then dimerizes and de-epoxidizes violaxanthin (Vx) to zeaxanthin (Zx) 5. The main NPQ component in plants is qE, which responds rapidly to changes in light intensity through protonation of the Photosystem II subunit PsbS 3 by the acidified lumen. This is visualized as the Non-Photochemical Quenching (NPQ) of chlorophyll fluorescence and comprises different components and underlying mechanisms, which were originally resolved in plants based on NPQ relaxation kinetics 2: transthylakoidal proton gradient (ΔpH)-dependent quenching (qE), state transitions (qT) and photoinhibition (qI). Most photosynthetic organisms face the same problem in strong light conditions: as the absorption of too much light energy can result in oxidative damage to the photosystem II (PSII) core, they must be capable of dissipating excess energy as heat 1.
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We observed that the suppression of NPQ by an uncoupler was due to an accelerated diatoxanthin epoxidation enzyme rather than to the usually hypothesized inhibition of the diadinoxanthin de-epoxidation enzyme. Our results demonstrate that a tight regulation of both enzymes is key to fine-tune NPQ: (i) the rate constant of diadinoxanthin de-epoxidation is low under a light-limiting regime but increases as photosynthesis saturates, probably due to the thylakoidal proton gradient ΔpH (ii) the rate constant of diatoxanthin epoxidation exhibits an optimum under low light and decreases in the dark due to an insufficiency of the co-factor NADPH as well as in higher light through an as yet unresolved inhibition mechanism, that is unlikely to be related to the ΔpH. From there, we explored the light-dependency of the activity of both enzymes. The proportionality between diatoxanthin and NPQ allowed us to calculate the activity of both xanthophyll cycle enzymes in the model diatom Phaeodactylum tricornutum from NPQ kinetics. Despite the xanthophyll cycle’s central role in photoprotection, its regulation is not yet well understood. The reverse reaction is performed by the diatoxanthin epoxidase. In most diatom species, NPQ is proportional to the concentration of the xanthophyll cycle pigment diatoxanthin formed from diadinoxanthin by the diadinoxanthin de-epoxidase enzyme. Feinglass, chief medical officer at Beckman Coulter.Diatoms possess an efficient mechanism to dissipate photons as heat in conditions of excess light, which is visualized as the Non-Photochemical Quenching of chlorophyll a fluorescence (NPQ). Testing for the antibodies, which create a built-in immunity, could help clear hospital staff, emergency responders and others to get back to work, indicating those who have had prior exposure and subsequent immunity to the disease, said Dr.
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Once the tests are finalized, Beckman Coulter said it intends to follow the FDA’s process established March 16 in response to the public health emergency. “This type of understanding could help determine … those who would require a vaccine once available or when an infected individual could safely return to work.”
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“Antibody assays play a critical role in understanding the measure of immunity an individual has developed against SARS-CoV-2,” said Kathleen Orland with Beckman Coulter’s chemistry and immunoassay business. Beckman Coulter in Brea developing coronavirus antibodies test – Orange County Register Close Menuīrea-based Beckman Coulter said Tuesday, March 31 it is developing tests, or assays, to identify antibodies created in people recovering from a novel coronavirus infection.