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The radioisotope 32Si was evaluated as a tracer for measuring silica production rates in marine waters. j2Si is a weak p-emitter that decays to 32P allowing the isotope to be used to determine simultaneously the production rate of biogenic silica and organic phosphorus. High specific activity '*Si, 42,000-52,000 Bq (pug Si)-I, was produced by the proton spallation of KCl. Reasonable tracer additions result in only nanomolar increases in the ambient silicic acid and orthophosphate concentrations during production rate experiments. Protocols for quantifying the amount of 32Si and 32P in samples by liquid scintillation counting (LSC) and gas-flow proportional counting (GFPC) are presented. Both protocols eliminate the 4-month wait for secular equilibrium between 32Si and 72P required by earlier methods. GFPC is especially useful as the instrumentation is lightweight and portable allowing real-time analysis of samples at sea. Real-time analysis by GFPC at sea and postcruise analysis by LSC gave results that agreed to within 17 and 7% for 12Si and 32e respectively. Subsequent intercalibrations of the LSC and GFPC methods indicated that agreement to within O.l-4% for both isotopes can be achieved. Parallel incubations of samples from Monterey Bay, California, using the radioisotope 32Si and the stable isotope 'OSi gave silica production rates that generally agreed to within 30%. No significant bias was observed between rates obtained with the two tracers. The greater sensitivity and ease of analysis of the radioisotope makes 32Si the tracer of choice for future studies of silica production in the ocean.

Our previous studies have demonstrated that long-term chemical contact with heterospecifics during development minimized unproductive heterospecific matings among the six Drosophila paulistorum semispecies. When socially isolated from conspecifics, discrimination significantly decreased so that more ultimately unproductive heterospecific matings occurred. Such results suggest that learning and social experiences play roles in mate recognition, using chemical information. In investigations into the development of discriminatory behavior in D. paulistorum, social experiences influence the production of cuticular hydrocarbons in both sexes among the six different semispecies of D. paulistorum. Produced by both sexes, 2-methyl triacontane has been detected from egg stages on, gradually increasing with age. However, 11-docosenyl acetate, a male pheromone, was not produced until early adult stages. There were consistent significant differences in quantities and ratios of each of these hydrocarbons among the six semispecies, contributing to their reproductive isolation. Furthermore, we found significant quantitative differences in hydrocarbons between socially isolated flies and communally raised ones: Socially isolated flies produced significantly greater quantities of hydrocarbons than communally raised flies, consistent with previous behavioral data, as isolated flies court more vigorously and often.

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The structure of phosmidosine (1), a novel proline-containing nucleotide antibiotic from Streptomyces durhameusis, active against the pathogenic fungus Botrytis cinerea, was determined by mass spectrometry and NMR spectroscopy. Homologs 2,3, and the isomer 4 were detected and characterized using approaches based principally on tandem mass spectrometry and combined liquid chromatography-mass spectrometry which permitted assignment of most structural features directly in the crude isolate without prior isolation of individual components. Conversion of 1-4 to the O-isopropylidene derivatives la-4a by a microscale procedure resulted in enhanced fast atom bombardment ionization (FAB) signal-to-background sensitivity. Collision-induced dissociation mass spectra were acquired from molecular ions and ion source-generated fragment ions and used in conjunction with FAB-deuterium exchange methods for the assignment of structural differences between la-4a.Phosmidosine is a new antifungal antibiotic recently isolated1 from culture filtrates of Streptomyces durhameusis. It exhibits specific inhibitory activity against spore formation of Botrytis cinerea, a world-wide pathogenic fungus which causes gray mold disease in a variety of fruits and vegetables. We report the structure of phosmidosine (1), the compound on which biological testing was carried out, and on two homologs (2, 3) and an isomer (4).Compared with a large number of known nucleoside antibiotics,3 four nucleotide antibiotics have been previously reported: agrocin-84 produced by Agrobacterium radiobacter,2 thuringiensin from Bacillus thuringiensis,3 fosfadecin from Pseudomonas viridiflava,4 and fosfocytocin from Pseudomonas fluorescens.* The culture fermentation conditions, isolation, microbiological properties, and a brief description of chemical properties of phosmidosine were published with an initial communication of structure l.1The structure determination of phosmidosine was hampered due to low isolation yield from fermentation cultures and chemical instability over a period of several weeks. As a consequence, much of the principal structural data were acquired using tandem mass spectrometry, which permitted a number of structural features of 1 and related compounds 2-4 to be deduced without chromatographic separation or prior isolation of individual components of the culture isolate. HPLC of a crude phosmidosine isolate, on which most mass spectrometry experiments were carried out, shows four principal constituents,5 corresponding to 1-4 as described in the following sections. Results and DiscussionThe exact molecular size and gross structural features of phosmidosine were established by high-resolution mass

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Methyl coenzyme M reductase (MCR) is a complex enzyme that catalyzes the final step in biological methanogenesis. To better understand its assembly, the recombinant MCR from the thermophile (rMCR) was expressed in the mesophile The rMCR was posttranslationally modified correctly and contained McrD and the unique nickel tetrapyrrole coenzyme F Subunits of the native (MCR) were largely absent, suggesting that the recombinant enzyme was formed by an assembly of cotranscribed subunits. Strong support for this hypothesis was obtained by expressing a chimeric operon comprising the His-tagged from and the from in The His-tagged purified rMCR then contained the McrA and the McrBDG. The present study prompted us to form a working model for MCR assembly, which can be further tested by the heterologous expression system established here. Approximately 1.6% of the net primary production of plants, algae, and cyanobacteria are processed by biological methane production in anoxic environments. This accounts for about 74% of the total global methane production, up to 25% of which is consumed by anaerobic oxidation of methane (AOM). Methyl coenzyme M reductase (MCR) is the key enzyme in both methanogenesis and AOM. MCR is assembled as a dimer of two heterotrimers, where posttranslational modifications and F cofactors are embedded in the active sites. However, this complex assembly process remains unknown. Here, we established a heterologous expression system for MCR to learn how MCR is assembled.