Exploring the interdependence of calcium and chloride activation of O2 evolution in photosystem II.

Calcium and chloride are activators of oxygen evolution in photosystem II (PSII), the light-absorbing water oxidase of higher plants, algae, and cyanobacteria. Calcium is an essential part of the catalytic Mn4CaO5 cluster that carries out water oxidation and chloride has two nearby binding sites, one of which is associated with a major water channel. The co-activation of oxygen evolution by the two ions is examined in higher plant PSII lacking the extrinsic PsbP and PsbQ subunits using a bisubstrate enzyme kinetics approach. Analysis of three different preparations at pH 6.3 indicates that the Michaelis constant, KM, for each ion is less than the dissociation constant, KS, and that the affinity of PSII for Ca2+ is about ten-fold greater than for Cl-, in agreement with previous studies. Results are consistent with a sequential binding model in which either ion can bind first and each promotes the activation by the second ion. At pH 5.5, similar results are found, except with a higher affinity for Cl- and lower affinity for Ca2+. Observation of the slow-decaying Tyr Z radical, YZ•, at 77 K and the coupled S2YZ• radical at 10 K, which are both associated with Ca2+ depletion, shows that Cl- is necessary for their observation. Given the order of electron and proton transfer events, this indicates that chloride is required to reach the S3 state preceding Ca2+ loss and possibly for stabilization of YZ• after it forms. Interdependence through hydrogen bonding is considered in the context of the water environment that intervenes between Cl- at the Cl-1 site and the Ca2+/Tyr Z region.

Universal and Serial Laboratory Testing for SARS-CoV-2 at a Long-Term Care Skilled Nursing Facility for Veterans - Los Angeles, California, 2020.

On March 28, 2020, two residents of a long-term care skilled nursing facility (SNF) at the Veterans Affairs Greater Los Angeles Healthcare System (VAGLAHS) had positive test results for SARS-CoV-2, the cause of coronavirus disease 2019 (COVID-19), by reverse transcription-polymerase chain reaction (RT-PCR) testing of nasopharyngeal specimens collected on March 26 and March 27. During March 29-April 23, all SNF residents, regardless of symptoms, underwent serial (approximately weekly) nasopharyngeal SARS-CoV-2 RT-PCR testing, and positive results were communicated to the county health department. All SNF clinical and nonclinical staff members were also screened for SARS-CoV-2 by RT-PCR during March 29-April 10. Nineteen of 99 (19%) residents and eight of 136 (6%) staff members had positive test results for SARS-CoV-2 during March 28-April 10; no further resident cases were identified on subsequent testing on April 13, April 22, and April 23. Fourteen of the 19 residents with COVID-19 were asymptomatic at the time of testing. Among these residents, eight developed symptoms 1-5 days after specimen collection and were later classified as presymptomatic; one of these patients died. This report describes an outbreak of COVID-19 in an SNF, with case identification accomplished by implementing several rounds of RT-PCR testing, permitting rapid isolation of both symptomatic and asymptomatic residents with COVID-19. The outbreak was successfully contained following implementation of this strategy.

Switching the Antidepressant After Nonresponse in Adults With Major Depression: A Systematic Literature Search and Meta-Analysis.

OBJECTIVE: Nonresponders to antidepressant monotherapy during acute treatment of major depression are often switched to a new antidepressant. The objective of this meta-analysis was to compare the efficacy of switching to a new antidepressant with continuation of the first antidepressant. DATA SOURCES: PubMed, Embase, PsycINFO, and Cochrane Central Register of Controlled Trials (CENTRAL) databases and additional sources were systematically searched independently by 2 authors up to March 2015 without language limitations. With employment of a sensitivity-enhancing search strategy, generic terms for major depression, switching, and randomized trials were combined. STUDY SELECTION: Articles (3,234) were screened for trials of patients with major depression who had not responded to antidepressant monotherapy who were then randomized either to a new antidepressant or to continuation of the first antidepressant. Studies were subdivided into those not allowing for dose escalation in the continuation arm (strict analysis) and those allowing for dose escalation (broad analysis). DATA EXTRACTION: Data were extracted and risk of bias was assessed independently by 2 authors, and data were pooled using random effects models. RESULTS: Four randomized controlled trials were included in the strict analysis and 8 in the broad analysis. In both analyses, switching was not superior to continuation: the standardized mean difference in the strict analysis was -0.17 (95% CI, -0.59 to 0.26; P = .45; I² = 77.8%) and in the broad analysis was 0.031 (95% CI, -0.26 to 0.32; P = .836; I² = 85.3%). All secondary outcome analyses (response and remission rates, low risk of bias studies only, leave-one-out analysis, dropouts) supported the results. There was no indication of publication bias. CONCLUSIONS: There is a dearth of randomized controlled trials investigating switching. There is no high-level evidence that switching the antidepressant is effective when compared to simply continuing the initial antidepressant. Since there are better treatment options than switching, physicians should be cautious to switch antidepressants.