Redox effects on the excited-state lifetime in chlorosomes and bacteriochlorophyll c oligomers

Oligomers of [E,E] BChl CF (8, 12-diethyl bacteriochlorophyll c esterified with farnesol (F)) and [Pr,E] BChl CF (analogously, M methyl, Pr propyl) in hexane and aqueous detergent or lipid micelles were studied by means of steady-state absorption, time-resolved fluorescence, and electron spin resonance spectroscopy. The maximum absorption wavelength, excited-state dynamics, and electron spin resonance (EPR) linewidths are similar to those of native and reconstituted chlorosomes of Chlorobium tepidum. The maximum absorption wavelength of oligomers of [E,E] BChl CF was consistently blue-shifted as compared to that of [Pr,E] BChl CF oligomers, which is ascribed to the formation of smaller oligomers with [E,E] BChl CF than [Pr,E] BChl CF. Time-resolved fluorescence measurements show an excited-state lifetime of 10 ps or less in nonreduced samples of native and reconstituted chlorosomes of Chlorobium tepidum. Under reduced conditions the excited-state lifetime increased to tens of picoseconds, and energy transfer to BChl a or long-wavelength absorbing BChl c was observed. Oligomers of [E,E] BChl CF and [Pr,E] BChl CF in aqueous detergent or lipid micelles show a similar short excited-state lifetime under nonreduced conditions and an increase up to several tens of picoseconds upon reduction. These results indicate rapid quenching of excitation energy in nonreduced samples of chlorosomes and aqueous BChl c oligomers. EPR spectroscopy shows that traces of oxidized BChl c radicals are present in nonreduced and absent in reduced samples of chlorosomes and BChl c oligomers. This suggests that the observed short excited-state lifetimes in nonreduced samples of chlorosomes and BChl c oligomers may be ascribed to excited-state quenching by BChl c radicals. The narrow EPR linewidth suggests that the BChl c are arranged in clusters of 16 and 6 molecules in chlorosomes of Chlorobium tepidum and Chloroflexus aurantiacus, respectively

Synthesis of chlorophyll b: Localization of chlorophyllide a oxygenase and discovery of a stable radical in the catalytic subunit

BACKGROUND: Assembly of stable light-harvesting complexes (LHCs) in the chloroplast of green algae and plants requires synthesis of chlorophyll (Chl) b, a reaction that involves oxygenation of the 7-methyl group of Chl a to a formyl group. This reaction uses molecular oxygen and is catalyzed by chlorophyllide a oxygenase (CAO). The amino acid sequence of CAO predicts mononuclear iron and Rieske iron-sulfur centers in the protein. The mechanism of synthesis of Chl b and localization of this reaction in the chloroplast are essential steps toward understanding LHC assembly. RESULTS: Fluorescence of a CAO-GFP fusion protein, transiently expressed in young pea leaves, was found at the periphery of mature chloroplasts and on thylakoid membranes by confocal fluorescence microscopy. However, when membranes from partially degreened cells of Chlamydomonas reinhardtii cw15 were resolved on sucrose gradients, full-length CAO was detected by immunoblot analysis only on the chloroplast envelope inner membrane. The electron paramagnetic resonance spectrum of CAO included a resonance at g = 4.3, assigned to the predicted mononuclear iron center. Instead of a spectrum of the predicted Rieske iron-sulfur center, a nearly symmetrical, approximately 100 Gauss peak-to-trough signal was observed at g = 2.057, with a sensitivity to temperature characteristic of an iron-sulfur center. A remarkably stable radical in the protein was revealed by an isotropic, 9 Gauss peak-to-trough signal at g = 2.0042. Fragmentation of the protein after incorporation of (125)I(- )identified a conserved tyrosine residue (Tyr-422 in Chlamydomonas and Tyr-518 in Arabidopsis) as the radical species. The radical was quenched by chlorophyll a, an indication that it may be involved in the enzymatic reaction. CONCLUSION: CAO was found on the chloroplast envelope and thylakoid membranes in mature chloroplasts but only on the envelope inner membrane in dark-grown C. reinhardtii cells. Such localization provides further support for the envelope membranes as the initial site of Chl b synthesis and assembly of LHCs during chloroplast development. Identification of a tyrosine radical in the protein provides insight into the mechanism of Chl b synthesis

Serum carboxyl-terminal propeptide of procollagen type I in exercise-induced left ventricular hypertrophy

Background: Left ventricular hypertrophy (LVH) induced by exercise is considered to be a physiologic adaptive mechanism without fibrogenic hyperactivity, as occurs in pathologic hypertrophy. Hypothesis: This study investigated serum markers of collagen synthesis and echo parameters of left ventricular diastolic function (LVdf) in 22 male athletes. Methods: Twenty-two highly competitive male athletes (10 cyclists, 12 soccer players) were studied with full history, clinical examination, Doppler echocardiogram, and serum concentration of the carboxyl-terminal propeptide of collagen type I (PIP). They were divided into two groups: normal left ventricular mass (N) with left ventricular mass index (LVMI) < 125 g/m2 (14 athletes) and LVH with LVMI > 125 g/m2 (8 athletes). Results: Age, body surface area, blood pressure, heart rate, and systolic function were not different between the groups. Serum concentration of PIP (N: 163 ± 44.1 µg/l, LVH: 172.7 ± 61.2 µg/l—NS) and LVdf (early to atrial peak mitral flow velocity ratio: [E/A] N:1.77 ± 0.47, LVH: 1.98 ± 0.70—NS, and early to atrial peak mitral annulus velocity ratio: [Ea/Aa] N: 2.63 ± 0.70, LVMI: 2.55 ± 0.90 LV1.61—NS) were similar in both groups. Conclusions: Normal serum concentration of PIP in athletes with LVH in association with normal LVdf indicates the possibility that in this type of physiologic hypertrophy there is mainly an increase of myocyte size without interstitial fibrosis.Facultad de Ciencias Médica

Leveraging the timing and frequency of patient decision aids in longitudinal shared decision‐making: A narrative review and applied model

Abstract Introduction Shared decision‐making (SDM) is intended to increase patient‐centredness of medical decision‐making for patients with acute and chronic conditions. Concurrently, patient decision aids (PtDAs) can supplement SDM by providing information to guide communication between patients and healthcare providers. Because of the prevalence of chronic conditions, where decisions may be extended or recurring, we sought to explore how effectively these tools have been leveraged in this context. Methods We conducted a narrative review of the literature on both SDM and PtDAs, searching PubMed and Boston University's library database search tool for English‐language articles published from January 2005 until March 2021. Additional search terms focused on temporality. Drawing from our findings, we developed a combined framework to highlight areas for future research using the discussion of end‐of‐life decisions as an exemplar to illustrate its relevance to chronic care contexts. Results After screening 57 articles, we identified 25 articles that fulfilled the inclusion criteria on SDM, PtDA use and temporality for chronic care. The literature on SDM highlighted time outside of the medical visit and opportunity to include outside decision partners as important elements of the process. PtDAs were commonly evaluated for process‐related and proximal outcomes, but less often for distal outcomes. Early evidence points to the value of comparative outcome evaluation based on the timing of PtDA distribution. Conclusion Our review of the literature on SDM and PtDAs reveals less attention to the timing of PtDAs relative to that of SDM. We highlight the need for further study of timing in PtDA use to improve longitudinal SDM for chronic care. The model that we propose in our discussion provides a starting point for future research on PtDA efficacy. Patient or Public Contribution Five patient consultants provided input and feedback on the development and utility of our model

A Cambialistic Superoxide Dismutase in the Thermophilic Photosynthetic Bacterium Chloroflexus aurantiacus

Superoxide dismutase from the thermophilic anoxygenic photosynthetic bacterium Chloroflexus aurantiacus was cloned, purified, and characterized. This protein is in the manganese- and iron-containing family of superoxide dismutases and is able to use both manganese and iron catalytically. This appears to be the only soluble superoxide dismutase in C. aurantiacus. Iron and manganese cofactors were identified by using electron paramagnetic resonance spectroscopy and were quantified by atomic absorption spectroscopy. By metal enrichment of growth media and by performing metal fidelity studies, the enzyme was found to be most efficient with manganese incorporated, yet up to 30% of the activity was retained with iron. Assimilation of iron or manganese ions into superoxide dismutase was also found to be affected by the growth conditions. This enzyme was also found to be remarkably thermostable and was resistant to H(2)O(2) at concentrations up to 80 mM. Reactive oxygen defense mechanisms have not been previously characterized in the organisms belonging to the phylum Chloroflexi. These systems are of interest in C. aurantiacus since this bacterium lives in a hyperoxic environment and is subject to high UV radiation fluxes