Enzymatic processing of pheromones and pheromone analogs

Summary Pheromone perception requires rapid enzymatic degradation of the active chemical signal in the sensory hairs. Three insects are used to illustrate chemical approaches to studying the degradation of pheromones by antennal enzymes. First, hydrolysis of acetate and haloacetate esters is examined in the diamondback moth,Plutella xylostella. Second, aldehyde oxidation and the selective inhibition of the oxidase and dehydrogenase activities are described for the tobacco budworm moth,Heliothis virescens. Finally, a stereochemical analysis of the epoxide-hydrase catalyzed addition of a water molecule to the oxirane ring of disparlure is described for the gypsy moth,Lymantria dispar.     

Covalently closed circles of adenovirus 5 DNA

The genome of adenoviruses is a double-stranded linear DNA molecule with inverted terminal repeats about 100 base pairs (bp) in length and a terminal protein covalently linked to the 5' nucleotide of each strand. Both of these features permit the formation of DNA circles, the inverted repeats allowing the circularization of single-stranded DNA and the terminal protein the joining of one or more molecules to yield double-stranded circles or concatemers. However, although the existence of covalently closed circles has been postulated, double-stranded viral DNA purified from virions or infected cells by conventional methods (that is, using proteases and phenol or chloroform) has always been obtained in a linear form. Here, we present evidence for the existence in adenovirus 5 (Ad5) infected cells of novel structures resulting from covalent head-to-tail joining of viral DNA molecules and show that these structures are due at least in part to the formation of covalently closed circles.     

Lack of effect of dihydroergotamine on endothelial and smooth muscle cell proliferation and endothelial cell prostanoid production

The most important effect of dihydroergotamine is venoconstriction, but certain metabolic effects and changes in vessel prostanoid activity have also been suggested. In this study endothelial cell production of 6-keto PGF1 alpha and TxB2 was quantitated in vitro. No evidence of altered prostanoid production was noted after incubation with dihydroergotamine (exposure ranging from 5 x 10(-3) to 5 x 10(-7) g/l). Similarly, no effect of dihydroergotamine on the growth rates of endothelial cells or smooth muscle cells in vitro was documented.     

Biochemistry: a cadmium enzyme from a marine diatom

The ocean biota contains a vast reservoir of genomic diversity. Here we present the sequence and preliminary characterization of a protein that is a cadmium-containing carbonic anhydrase from the marine diatom Thalassiosira weissflogii. The existence of a cadmium enzyme in marine phytoplankton may indicate that there is a unique selection pressure for metalloenzymes in the marine environment, and our discovery provides a long-awaited explanation for the nutrient-like behaviour of cadmium in the oceans.     

Two-dimensional spectroscopy of electronic couplings in photosynthesis

Time-resolved optical spectroscopy is widely used to study vibrational and electronic dynamics by monitoring transient changes in excited state populations on a femtosecond timescale. Yet the fundamental cause of electronic and vibrational dynamics--the coupling between the different energy levels involved--is usually inferred only indirectly. Two-dimensional femtosecond infrared spectroscopy based on the heterodyne detection of three-pulse photon echoes has recently allowed the direct mapping of vibrational couplings, yielding transient structural information. Here we extend the approach to the visible range and directly measure electronic couplings in a molecular complex, the Fenna-Matthews-Olson photosynthetic light-harvesting protein. As in all photosynthetic systems, the conversion of light into chemical energy is driven by electronic couplings that ensure the efficient transport of energy from light-capturing antenna pigments to the reaction centre. We monitor this process as a function of time and frequency and show that excitation energy does not simply cascade stepwise down the energy ladder. We find instead distinct energy transport pathways that depend sensitively on the detailed spatial properties of the delocalized excited-state wavefunctions of the whole pigment-protein complex.     

Tunable gold catalysts for selective hydrocarbon oxidation under mild conditions

Oxidation is an important method for the synthesis of chemical intermediates in the manufacture of high-tonnage commodities, high-value fine chemicals, agrochemicals and pharmaceuticals: but oxidations are often inefficient. The introduction of catalytic systems using oxygen from air is preferred for 'green' processing. Gold catalysis is now showing potential in selective redox processes, particularly for alcohol oxidation and the direct synthesis of hydrogen peroxide. However, a major challenge that persists is the synthesis of an epoxide by the direct electrophilic addition of oxygen to an alkene. Although ethene is epoxidized efficiently using molecular oxygen with silver catalysts in a large-scale industrial process, this is unique because higher alkenes can only be effectively epoxidized using hydrogen peroxide, hydroperoxides or stoichiometric oxygen donors. Here we show that nanocrystalline gold catalysts can provide tunable active catalysts for the oxidation of alkenes using air, with exceptionally high selectivity to partial oxidation products ( approximately 98%) and significant conversions. Our finding significantly extends the discovery by Haruta that nanocrystalline gold can epoxidize alkenes when hydrogen is used to activate the molecular oxygen; in our case, no sacrificial reductant is needed. We anticipate that our finding will initiate attempts to understand more fully the mechanism of oxygen activation at gold surfaces, which might lead to commercial exploitation of the high redox activity of gold nanocrystals.