Synthesis of selenocysteine and its derivatives with an emphasis on selenenylsulfide (-Se-S-) formation

A short survey of historic and current methods for the synthesis of selenocysteine, selenocystine, and derivatives and related compounds is presented, with an additional emphasis on the formation of selenocysteine-derived Se-S bridges. The majority of methods to the amino acid starts with protected and O-activated serine, but also other concepts are included such as radical or multicomponent strategies, the latter allowing also direct access to peptoids in one pot. Of special importance is the monomeric oxidative cyclization of selenocysteine-cysteine peptides to eight-membered and larger rings with a selenenylsulfide bridge, a crucial element in several selenoproteins.     

Environmental Indication: A Field Test of an Ecosystem Approach to Quantify Biological Self-Organization

In this study, we take an ecosystem approach to examine the degree of biological self-organization at the ecosystem level. An integrated set of indicators is derived from a theoretical framework and tested by field data from an ecosystem research project focusing on the Bornhöved Lake district in northern Germany. This field test is based on a comparison of the self-organized phenomena that comprise the carbon, water, and energy budgets of two adjacent edaphically and climatically similar ecosystems, that have vastly different levels of human interference—a crop field and a beech forest. In terms of biomass storage, biologically incorporated nitrogen and phosphorus, species number, total ecosystem respiration per total biomass (qCO₂), total ecosystem assimilation per available nutrients, and transpiration per total evapotranspiration, we found clear differences between the systems. Ecosystem surface temperature and R_n/K* were found to be of limited utility in characterizing the two systems. The study is rooted in the concept of ecological integrity, an influential idea at the interface of ecological and environmental debate that has acquired a number of different meanings. Among other interpretations, it can be viewed as a guiding principle for sustainable land use that aims at long-term protection of ecological life-support systems. Effective use of any interpretation of this concept requires a theoretically consistent and applicable set of indicators. Therefore, we also discuss the integration of the indicator set and its potential use in monitoring programs.     

Clathrin‐Dependent or Not: Is It Still the Question?

Whether the endocytic uptake of a given molecule is mediated through clathrin-coated pits or not is a classical criterion used to characterize its endocytic pathway(s). Hence, clathrin-dependent endocytosis has been associated with highly selective and efficient uptake, whereas clathrin-independent endocytosis appeared to be confined to bulk uptake of fluid-phase markers. This scholastic view has recently been challenged using newly developed molecular tools that allow for the first time a functional and mechanistic analysis of these less well-characterized clathrin-independent pathways, including caveolar uptake and macropinocytosis. Furthermore, several studies point to a critical role of lateral lipid asymmetry – lipid rafts/microdomains – in membrane sorting. We will discuss the potential role of these structures in endocytosis and the possibility that differential sorting at the plasma membrane predisposes the ensuing intracellular fate of a given molecule as well as its physiological function.     

Differential accumulation of xanthones in methyl-jasmonate- and yeast-extract-treated cell cultures of Centaurium erythraea and Centaurium littorale

Cell-suspension cultures of Centaurium erythraea and Centaurium littorale (Gentianaceae) respond to methyl jasmonate and yeast extract with a differential accumulation of xanthones. Methyl jasmonate induced the formation of 1-hydroxy-3,5,6,7-tetramethoxyxanthone, the amount of which increased in both cell cultures around 10 h after addition. A substantial increase in the activity of phenylalanine ammonia-lyase (PAL) was not observed. When challenged with yeast extract the cell cultures accumulated l,5-dihydroxy-3-methoxyxanthone. This appeared rapidly after addition of yeast extract in C. erythraea but its amount in C. littorale increased only after a lag phase of 25 h. While PAL activity in C. erythraea was strongly suppressed a fourfold increase in its activity was found in C. littorale. Both elicited xanthones accumulated intracellularly. A scheme for xanthone biosynthesis in the two cell cultures is proposed.     

Pyrrolizidine alkaloids: different acquisition and use patterns in Apocynaceae and Solanaceae feeding ithomiine butterflies (Lepidoptera: Nymphalidae)

Pyrrolizidine alkaloids (PAs) often serve as chemical mediators of plant-herbivore-predator interactions. Butterflies (Danainae and Ithomiinae) and moths (Arctiidae) usually acquire PAs from plant sources (larval host plants, flowers or withered leaves visited by adults—pharmacophagy) and thereby become chemically protected against predators; they also use PAs as pheromone precursors. Study by GC-MS of PAs in three species of Ithomiinae butterflies, their larval host plants and adult alkaloid sources showed three different acquisition patterns: (1) larvae of the primitive Tithorea harmonia sequester PAs from their food plant Prestonia acutifolia (Apocynaceae: Echitoideae), and adults may also acquire these alkaloids from plant sources; (2) larvae of the more derived Aeria olena feed on Prestonia coalita , in whose leaves no PAs were detected, but freshly emerged adults sometimes contain PAs and males intensively seek and sequester these alkaloids in plant sources; and (3) larvae of the still more advanced Mechanitis polymnia feed on several PA-free Solanum species, and adult males sequester the alkaloids from various plant sources. Males and females of all three species contain mostly two PAs, the diastereoisomeric retronecine monoesters lycopsamine and intermedine, stored in the N-oxide form. Larval host plants and adult plant sources showed a large array of PA structures, the most abundant and frequent being lycopsamine and its diastereoisomers intermedine, echinatine, rinderine and indicine, and the deoxy-analogues supinine and amabiline. Bioassays with wild caught and freshly emerged adults suggest that protection against predation by the orb weaving spider Nephila clavipes may be dependent on PA concentration and maybe some spider idiosyncrasies, but freshly emerged Aeria olena without PAs are also liberated by Nephila , suggesting other protective compounds. The role of this spider as a selective pressure for PA acquisition by ithomiines is not clear.     

Effects of light on protein secretion in Neurospora crassa

The relative concentrations of secreted proteins in liquid cultures of Neurospora crassa differ in constant darkness compared to constant light (2500lx). Light reduces the concentrations of some polypeptides markedly and increases the concentrations of protein species of 67, 40, 18 and 13 kDa. The blind wc-2 mutant of Neurospora does not show light dependent differences in amounts of secreted proteins. One of the light-sensitive extracellular proteins is shown to be a protease of 17,5 kDa.