Evolution,pollination, and systematics of the tribeNeottieae (Orchidaceae)

The various classifications of the orchid tribeNeottieae are reviewed and a new classification is proposed that divides the tribe into three subtribes,Neottiinae, Limodorinae, andCephalantherinae, based primarily on characters of the column (gynostemium). A cladistic analysis illustrates that these three subtribes are more closely related to one another than either is to any other group in subfam.Neottioideae, although there are very few apomorphic characters for the tribe. Pollination biology is also discussed showing links between breeding systems and distribution. There is also a possible role between column and labellum morphology and the emergence of a deceptive pollination syndrome from one of reward.     

A flash-photolysis study of the reactions of acaa 3-ttype cytochrome oxidase with dioxygen and carbon monoxide

The time course of absorbance changes following flash photolysis of the fully-reduced carboxycytochrome oxidase fromBacillus PS3 in the presence of O₂ has been followed at 445, 550, 605, and 830 nm, and the results have been compared with the corresponding changes in bovine cytochrome oxidase. The PS3 enzyme has a covalently bound cytochromec subunit and the fully-reduced species therefore accommodates five electrons instead of four as in the bovine enzyme. In the bovine enzyme, following CO dissociation, four phases were observed with time constants of about 10 s, 30 s, 100 s, and 1 ms at 445 nm. The initial, 10-s absorbance change at 445 nm is similar in the two enzymes. The subsequent phases involving hemea and Cu_A are not seen in the PS3 enzyme at 445 nm, because these redox centers are re-reduced by the covalently bound cytochromec, as indicated by absorbance changes at 550 nm. A reaction scheme consistent with the experimental observations is presented. In addition, internal electron-transfer reactions in the absence of O₂ were studied following flash-induced CO dissociation from the mixed-valence enzyme. Comparisons of the CO recombination rates in the mixed-valence and fully-reduced oxidases indicate that more electrons were transferred from hemea ₃ toa in PS3 oxidase compared to the bovine enzyme.     

Aspartic proteinases: Fourier transform infrared spectroscopic studies of a model of the active side.

We synthesized and studied by Fourier transform infrared spectroscopy nine monosalts of diamides as models for the active side of aspartic proteinases. One compound, the monosalt of meta-aminobenzoic acid diamide of fumaric acid (m-FUM), shows the same biological activity as pepsin with regard to the splitting of peptide bonds of the Pro-Thi-Glu-Phe-Phe(4-NO2)-Arg-Leu heptapeptide. The monosalt of m-FUM forms with oxindole a complex in which the carboxylic acid group of the monosalt of m-FUM is strongly hydrogen bonded with the O atom of the peptide bond of oxindole. When one water molecule is added to this complex, the strong field of the carboxylate group destabilizes an O-H bond of the water molecule. The distorted water molecule attacks the carbon atom of the peptide group, and the water proton transfers to the peptide N atom. Simultaneously, the C-N bond of the amide group is broken. Hence it is demonstrated that the catalytic mechanism of aspartic acid proteinases is a base catalysis. The results show that for this catalytic mechanism there are sufficient carboxylic and carboxylate groups, as well as a water molecule in the correct arrangement. It was also demonstrated with other monosalts of dicarboxylic acids that well-defined steric conditions of the carboxylic acid and the carboxylate group must be fulfilled to show hydrolytic activity with regard to oxindole molecules.     

Analysis of viability and cell types of macroalgal protoplasts using flow cytometry

The ability to rapidly distinguish viable sub-populations of cells within populations of macroalgal protoplast isolations was demonstrated using flow cytometry. Viable protoplasts from Ulva sp. and Porphyra perforata J. Ag. were distinguished from non-viable protoplasts based on differential fluorescein accumulation. The identities of cortical and epidermal protoplasts from Macrocystis pyrifera (L.) C. Ag. were inferred based on light-scattering and chlorophyll a autofluorescence. Three cell types could be distinguished among protoplasts released from thalli of P. perforata based on chlorophyll a and phycoerythrin autofluorescence. Mixed protoplast populations of Ulva sp. and P. perforata were also discernable based on relative chlorophyll a and phycoerythrin autofluorescence. The ability to screen heterogenous protoplast populations rapidly, combined with the cell sorting capabilities of many flow cytometers, should prove valuable for seaweed biotechnology.     

Quantifying marine snow as a food choice for zooplankton using stable silicon isotope tracers

Aggregates of biogenic origin >0.5 mm, known as marine snow,represent a concentrated potential source of food for zooplankton.Little is known, however, about whether aggregates are commonlygrazed by zooplankton in the field. While previous laboratorystudies have shown that the euphausiid Euphausia pacifica, andthe copepod, Calanus pacificus, common crustacean zooplankters,consume marine snow if it is the only food source available,it is not known if euphausiids will select marine snow in thepresence of edible dispersed cells, as readily occurs in nature.To examine this question, we offered E. pacifica the diatom,Nitzschia angularis in aggregated and dispersed form as preysimultaneously. Aggregates and dispersed food contained identicalcell types so that differing prey quality, taste or motilitywould not be a factor. A new method was developed to track foodsources by labeling the frustules of aggregated cells with differentnaturally occurring, but rare, stable isotopes of silicon, ³⁰Siand ²⁹Si. Food selection was then estimated by measuring theisotopic composition of silica within fecal pellets producedby animals feeding on mixtures of the two labeled foods. Resultsindicate that E. pacifica consumed both aggregates and dispersedcells, even when more cells were made available in dispersedform than in aggregated form. This suggests that aggregatesmay indeed be a food source in the field, even when dispersedcells are relatively abundant. The method of labeling diatomcells with stable isotopes of silica may prove useful for futuregrazing experiments to distinguish identical cell types.     

Covid‐19.bioreproducibility.org: A web resource for SARS‐CoV‐2‐related structural models

The COVID‐19 pandemic has triggered numerous scientific activities aimed at understanding the SARS‐CoV‐2 virus and ultimately developing treatments. Structural biologists have already determined hundreds of experimental X‐ray, cryo‐EM, and NMR structures of proteins and nucleic acids related to this coronavirus, and this number is still growing. To help biomedical researchers, who may not necessarily be experts in structural biology, navigate through the flood of structural models, we have created an online resource, covid19.bioreproducibility.org, that aggregates expert‐verified information about SARS‐CoV‐2‐related macromolecular models. In this article, we describe this web resource along with the suite of tools and methodologies used for assessing the structures presented therein.     

Identification of a cytochrome bc1-aa3 supercomplex in Rhodobacter sphaeroides

Respiration is carried out by a series of membrane-bound complexes in the inner mitochondrial membrane or in the cytoplasmic membrane of bacteria. Increasing evidence shows that these complexes organize into larger supercomplexes. In this work, we identified a supercomplex composed of cytochrome (cyt.) bc₁ and aa₃-type cyt. c oxidase in Rhodobacter sphaeroides. We purified the supercomplex using a His-tag on either of these complexes. The results from activity assays, native and denaturing PAGE, size exclusion chromatography, electron microscopy, optical absorption spectroscopy and kinetic studies on the purified samples support the formation and coupled quinol oxidation:O₂ reduction activity of the cyt. bc₁-aa₃ supercomplex. The potential role of the membrane-anchored cyt. c_y as a component in supercomplexes was also investigated.