(S)- and (R)-eriodictyol-6-C-beta-D-glucopyranoside, novel keys to the fermentation of rooibos (Aspalathus linearis)

The processed leaves and stems of Aspalathus linearis contain a new diastereomeric pair of the flavanones, (S)- and (R)-eriodictyol-6-C-beta-D-glucopyranoside, which is also formed via the oxidative cyclization of the dihydrochalcone, aspalathin, under conditions which mimic the fermentation process.     

The endocytic protein intersectin is a major binding partner for the Ras exchange factor mSos1 in rat brain

We recently identified intersectin, a protein containing two EH and five SH3 domains, as a component of the endocytic machinery. The N-terminal SH3 domain (SH3A), unlike other SH3 domains from intersectin or various endocytic proteins, specifically inhibits intermediate events leading to the formation of clathrin-coated pits. We have now identified a brain-enriched, 170 kDa protein (p170) that interacts specifically with SH3A. Screening of combinatorial peptides reveals the optimal ligand for SH3A as Pp(V/I)PPR, and the 170 kDa mammalian son-of-sevenless (mSos1) protein, a guanine-nucleotide exchange factor for Ras, con- tains two copies of the matching sequence, PPVPPR. Immunodepletion studies confirm that p170 is mSos1. Intersectin and mSos1 are co-enriched in nerve terminals and are co-immunoprecipitated from brain extracts. SH3A competes with the SH3 domains of Grb2 in binding to mSos1, and the intersectin-mSos1 complex can be separated from Grb2 by sucrose gradient centrifugation. Overexpression of the SH3 domains of intersectin blocks epidermal growth factor-mediated Ras activation. These results suggest that intersectin functions in cell signaling in addition to its role in endocytosis and may link these cellular processes.     

Mathematical simulation of the diel O, S, and C biogeochemistry of a hypersaline microbial mat

The creation of a mathematical simulation model of photosynthetic microbial mats is important to our understanding of key biogeochemical cycles that may have altered the atmospheres and lithospheres of early Earth. A model is presented here as a tool to integrate empirical results from research on hypersaline mats from Baja California Sur (BCS), Mexico into a computational system that can be used to simulate biospheric inputs of trace gases to the atmosphere. The first version of our model, presented here, calculates fluxes and cycling of O(2), sulfide, and dissolved inorganic carbon (DIC) via abiotic components and via four major microbial guilds: cyanobacteria (CYA), sulfate reducing bacteria (SRB), purple sulfur bacteria (PSB) and colorless sulfur bacteria (CSB). We used generalized Monod-type equations that incorporate substrate and energy limits upon maximum rates of metabolic processes such as photosynthesis and sulfate reduction. We ran a simulation using temperature and irradiance inputs from data collected from a microbial mat in Guerrero Negro in BCS (Mexico). Model O(2), sulfide, and DIC concentration profiles and fluxes compared well with data collected in the field mats. There were some model-predicted features of biogeochemical cycling not observed in our actual measurements. For instance, large influxes and effluxes of DIC across the MBGC mat boundary may reveal previously unrecognized, but real, in situ limits on rates of biogeochemical processes. Some of the short-term variation in field-collected mat O(2) was not predicted by MBGC. This suggests a need both for more model sensitivity to small environmental fluctuations for the incorporation of a photorespiration function into the model.     

Circular dichroism, a powerful tool for the assessment of absolute configuration of flavonoids

Circular dichroism is a powerful tool for establishing the absolute configuration of flavonoids and proanthocyanidin analogues. It has been utilized to study the configuration of flavanones, dihydroflavonols (3-hydroxyflavanones), flavan-3-ols, flavan-4-ols, flavan-3,4-diols, flavans, isoflavans, isoflavanones, pterocarpans, 6a-hydroxypterocarpans, rotenoids, 12a-hydroxyrotenoids, neoflavonoids, 3,4-dihydro-4-arylcoumarins, 4-arylflavan-3-ols, auronols, homoisoflavanones, proanthocyanidins, and various classes of biflavonoids. Results relevant to the correlation of circular dichroic data and the absolute configuration of the diastereoisomers of some of the above classes of compounds will be discussed.     

Immunological relevance of malonic dialdehyde I. Preparation of Schiff''s bases from lysozyme or polylysine reacted with malonic dialdehyde

Malonic dialdehyde (MDA) is produced in all mammalian tissues either as an end product of lipid peroxidation or as a by-product of arachidonic acid metabolism. It may either be quickly oxidized to carbon dioxide or combine covalently with primary amino groups of proteins, phospholipids or nucleic acids. In the latter case, fluorescent Schiff's bases with 1-amino-3-iminopropene (AIP) bridges are produced. MDA metabolism is now fairly well elucidated, while that of MDA-cross-linked biological molecules remains unknown. Aiming at investigating the fate of such cross-linked molecules in mammalian organisms, and their biological relevance, we tried in the present study to prepare reproducibly Schiff's bases from chicken egg white lysozyme reacted with MDA. The resulting mixture of different Schiff's bases (ML) was fractionated into single oligomeric fractions by gel-filtration chromatography. ML and the single oligomeric fractions obtained from this mixture were controlled by fluorescence measurements for their content of AIP bridges, and by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) for their content of different oligomers. ML contained monomers, dimers, trimers and other oligomers, as shown by SDS-PAGE. The corresponding single oligomeric fractions were satisfactorily separated by gel-filtration chromatography (purity better than 94%, as determined by SDS-PAGE). Schiff's bases from poly-L-lysine reacted with MDA (MP) were also prepared. Their fluorescence emission spectrum was similar to that of ML and to that of the single oligomeric fractions obtained from ML.