Probing the role of Valine 185 of the D1 protein in the Photosystem II oxygen evolution

In Photosystem II (PSII), the Mn₄CaO₅-cluster of the active site advances through five sequential oxidation states (S₀ to S₄) before water is oxidized and O₂ is generated. The V185 of the D1 protein has been shown to be an important amino acid in PSII function (Dilbeck et al. Biochemistry 52 (2013) 6824–6833). Here, we have studied its role by making a V185T site-directed mutant in the thermophilic cyanobacterium Thermosynechococcus elongatus. The properties of the V185T-PSII have been compared to those of the WT*3-PSII by using EPR spectroscopy, polarography, thermoluminescence and time-resolved UV–visible absorption spectroscopy. It is shown that the V185 and the chloride binding site very likely interact via the H-bond network linking Tyr_Z and the halide. The V185 contributes to the stabilization of S₂ into the low spin (LS), S?=?1/2, configuration. Indeed, in the V185T mutant a high proportion of S₂ exhibits a high spin (HS), S?=?5/2, configuration. By using bromocresol purple as a dye, a proton release was detected in the S₁Tyr_Z?→?S₂^HSTyr_Z transition in the V185T mutant in contrast to the WT*3-PSII in which there is no proton release in this transition. Instead, in WT*3-PSII, a proton release kinetically much faster than the S₂^LSTyr_Z?→?S₃Tyr_Z transition was observed and we propose that it occurs in the S₂^LSTyr_Z?→?S₂^HSTyr_Z intermediate step before the S₂^HSTyr_Z?→?S₃Tyr_Z transition occurs. The dramatic slowdown of the S₃Tyr_Z?→?S₀Tyr_Z transition in the V185T mutant does not originate from a structural modification of the Mn₄CaO₅ cluster since the spin S?=?3?S₃ EPR signal is not modified in the mutant. More probably, it is indicative of the strong implication of V185 in the tuning of an efficient relaxation processes of the H-bond network and/or of the protein.     

A trans‐Atlantic examination of haddock Melanogrammus aeglefinus food habits

The food habits of Melanogrammus aeglefinus were explored and contrasted across multiple north‐eastern and north‐western Atlantic Ocean ecosystems, using databases that span multiple decades. The results show that among all ecosystems, echinoderms are a consistent part of M. aeglefinus diet, but patterns emerge regarding where and when M. aeglefinus primarily eat fishes v. echinoderms. Melanogrammus aeglefinus does not regularly exhibit the increase in piscivory with ontogeny that other gadoids often show, and in several ecosystems there is a lower occurrence of piscivory. There is an apparent inverse relationship between the consumption of fishes and echinoderms in M. aeglefinus over time, where certain years show high levels of one prey item and low levels of the other. This apparent binary choice can be viewed as part of a gradient of prey options, contingent upon a suite of factors external to M. aeglefinus dynamics. The energetic consequences of this prey choice are discussed, noting that in some instances it may not be a choice at all.     

The pecking order of skin Advanced Glycation Endproducts (AGEs) as long-term markers of glycemic damage and risk factors for micro- and subclinical macrovascular disease progression in Type 1 diabetes

To date more than 20 glycation products were identified, of which ~15 in the insoluble human skin collagen fraction. The goal of this review is to streamline 30 years of research and ask a set of important questions: in Type 1 diabetes which glycation products correlate best with 1) past mean glycemia 2) reversibility with improved glycemic control, 2) cross-sectional severity of retinopathy, nephropathy and neuropathy and 3) the future long-term risk of progression of micro- and subclinical macrovascular disease. The trio of glycemia related glycation markers furosine (FUR)/fructose-lysine (FL), glucosepane and methylglyoxal hydroimidazolone (MG-H1) emerges as extraordinarily strong predictors of existing and future microvascular disease progression risk despite adjustment for both past and prospective A1c levels. X² values are up to 25.1, p values generally less than 0.0001, and significance remains after adjustment for various factors such as A1c, former treatment group, log albumin excretion rate, abnormal autonomic nerve function and LDL levels at baseline. In contrast, subclinical cardiovascular progression is more weakly correlated with AGEs/glycemia with X² values?<?5.0 and p values generally <?0.05 after all adjustments. Except for future carotid intima-media thickness, which correlates with total AGE burden (MG-H1, pentosidine, fluorophore LW-1 and decreased collagen solubility), adjusted FUR and Collagen Fluorescence (CLF) are the strongest markers for future coronary artery calcium deposition, while cardiac hypertrophy is associated with LW-1 and CLF adjusted for A1c. We conclude that a robust clinical skin biopsy AGE risk panel for microvascular disease should include at least FUR/FL, glucosepane and MG-H1, while a macrovascular disease risk panel should include at least FL/FUR, MG-H1, LW-1 and CLF.     

Callus induction, somatic embryogenesis and organogenesis in Narcissus confusus: correlation between the state of differentiation and the content of galanthamine and related alkaloids

In vitro cultures from two strains of Narcissus confusus (Amaryllidaceae) initiated from mature seeds were screened for their ability to produce alkaloids. Protocols for callus induction, somatic embryogenesis and organogenesis were established. The alkaloid contents were determined by HPLC. Undifferentiated calli produced small amounts of galanthamine, which increased with the degree of tissue differentiation. Scanning electron micrographs of the cultures at different stages of development were made. Embryogenic friable calli were maintained in culture for more than 2 years, retaining a high regeneration capability. All regenerated plants showed normal morphological characteristics. Received: 20 August 1997 / Revision received: 20 December 1997 / Accepted: 1 February 1998