C, N, and noble gas isotopes in grain size separates of presolar diamonds from Efremovka.

Nanometer-size presolar diamonds from the Efremovka CV3 chondrite were physically separated into several grain size fractions by ultracentrifugation. The coarsest size fraction is the most enriched in carbon-12; the others have broadly similar carbon isotopic compositions. Measurement of noble gases shows that their concentration decreases with decreasing grain size. This effect is attributed to ion implantation. Such an episode could occur in the envelope of a supernova that produced the diamonds, or in interstellar space; in either case, ions with energies above a certain threshold pass completely through the smaller diamond grains without being captured. Concentrations of nitrogen show only minor variations with grain size, indicating a different mechanism of incorporation into the diamonds.

On the attempts to measure water (and other volatiles) directly at the surface of a comet.

The Ptolemy instrument on the Philae lander (of the Rosetta space mission) was able to make measurements of the major volatiles, water, carbon monoxide and carbon dioxide, directly at the surface of comet 67P/Churyumov-Gerasimenko. We give some background to the mission and highlight those instruments that have already given insights into the notion of water in comets, and which will continue to do so as more results are either acquired or more fully interpreted. On the basis of our results, we show how comets may in fact be heterogeneous over their surface, and how surface measurements can be used in a quest to comprehend the daily cycles of processes that affect the evolution of comets.This article is part of the themed issue 'The origin, history and role of water in the evolution of the inner Solar System'.

COMETARY SCIENCE. CHO-bearing organic compounds at the surface of 67P/Churyumov-Gerasimenko revealed by Ptolemy.

The surface and subsurface of comets preserve material from the formation of the solar system. The properties of cometary material thus provide insight into the physical and chemical conditions during their formation. We present mass spectra taken by the Ptolemy instrument 20 minutes after the initial touchdown of the Philae lander on the surface of comet 67P/Churyumov-Gerasimenko. Regular mass distributions indicate the presence of a sequence of compounds with additional -CH2- and -O- groups (mass/charge ratios 14 and 16, respectively). Similarities with the detected coma species of comet Halley suggest the presence of a radiation-induced polymer at the surface. Ptolemy measurements also indicate an apparent absence of aromatic compounds such as benzene, a lack of sulfur-bearing species, and very low concentrations of nitrogenous material.

A nitrogen and argon stable isotope study of Allan Hills 84001: implications for the evolution of the Martian atmosphere.

The abundances and isotopic compositions of N and Ar have been measured by stepped combustion of the Allan Hills 84001 (ALH 84001) Martian orthopyroxenite. Material described as shocked is N-poor ([N] approximately 0.34 ppm; delta 15N approximately +23%); although during stepped combustion, 15N-enriched N (delta 15N approximately +143%) is released in a narrow temperature interval between 700 degrees C and 800 degrees C (along with 13C-enriched C (delta 13C approximately +19%) and 40Ar). Cosmogenic species are found to be negligible at this temperature; thus, the isotopically heavy component is identified, in part, as Martian atmospheric gas trapped relatively recently in the history of ALH84001. The N and Ar data show that ALH84001 contains species from the Martian lithosphere, a component interpreted as ancient trapped atmosphere (in addition to the modern atmospheric species), and excess 40Ar from K decay. Deconvolution of radiogenic 40Ar from other Ar components, on the basis of end-member 36Ar/14N and 40Ar/36Ar ratios, has enabled calculation of a K-Ar age for ALH 84001 as 3.5-4.6 Ga, depending on assumed K abundance. If the component believed to be Martian palaeoatmosphere was introduced to ALH 84001 at the time the K-Ar age was set, then the composition of the atmosphere at this time is constrained to: delta 15N > or = +200%, 40Ar/36Ar < or = 3000 and 36Ar/14N > or = 17 x 10(-5). In terms of the petrogenetic history of the meteorite, ALH 84001 crystallised soon after differentiation of the planet, may have been shocked and thermally metamorphosed in an early period of bombardment, and then subjected to a second event. This later process did not reset the K-Ar system but perhaps was responsible for introducing (recent) atmospheric gases into ALH 84001; and it might mark the time at which ALH 84001 suffered fluid alteration resulting in the formation of the plagioclase and carbonate mineral assemblages.

Beagle 2: a proposed exobiology lander for ESA's 2003 Mars Express mission.

The aim of the proposed Beagle 2 small lander for ESA's 2003 Mars Express mission is to search for organic material on and below the surface of Mars and to study the inorganic chemistry and mineralogy of the landing site. The lander will have a total mass of 60kg including entry, descent, and landing system. Experiments will be deployed on the surface using a robotic arm. It will use a mechanical mole and grinder to obtain samples from below the surface, under rocks, and inside rocks. Sample analysis by a mass spectrometer will include isotopic analysis. An optical microscope, an X-ray spectrometer and a Mossbauer spectrometer will conduct in-situ rock studies.

Human toxocariasis and direct contact with dogs.

Toxocariasis in man is traditionally thought to be contracted through the ingestion of eggs from contaminated soil. The disease may manifest itself in different syndromes such as ocular larval migrans, visceral larval migrans and covert toxocariasis. This paper assesses the evidence for the soil contamination hypothesis and proposes that direct contact with dogs may provide a better explanation of the epidemiology of the disease. Hair was collected from 60 dogs from various places in Ireland and the UK and examined for the presence of Toxocara canis eggs. T. canis eggs were found in the hair of 25 per cent of the dogs; in total, 71 eggs were recovered, of which 4.2 per cent were embryonated and 23.9 per cent were embryonating. The maximum densities of the embryonating and embryonated eggs were 180 and 20 eggs per gram of hair, respectively, much higher than the densities reported for soil samples. It is suggested that dogs infected with T. canis may infect people by direct contact.

Meteorites, Mars and Beagle 2--from novel analysis in the laboratory to pioneering experiments in space.

On 25 December 2003, the British-built Beagle 2 probe will land on the surface of Mars to carry out one of the most potentially important pieces of analytical science ever conceived: to search for evidence of extra terrestrial life. Dr Ian Wright of the Open University talks us through the difficulties of performing measurements in such a harsh environment.

Simple efficient methods for the isolation of malate dehydrogenase from thermophilic and mesophilic bacteria.

Malate dehydrogenase from a number of bacteria drawn from several genera and representing the mesophilic, moderately thermophilic and extremely thermophilic classes was isolated by procedures which involve only a small number of steps (in most cases only two), of which the key one is affinity chromatography on 5'-AMP--Sepharose and/or on NAD+--hexane--agarose. Electrophoretic analysis of the native enzymes in polyacrylamide gel and of the denaturated enzymes in sodium dodecyl sulphate/polyacrylamide gel revealed no significant protein impurity in the purified preparations. The yields ranged from about 40% to over 80%. The malate dehydrogenases from the extreme thermophiles and from some of the moderate thermophiles are appreciably less efficient catalytically than their mesophilic homologues.

A microprocessor based photoplethysmograph for use in clinical practice.

A microprocessor-based system of photoplethysmography and its use in measuring skin blood flow is described. The system was designed specifically for use over long periods and for the analysis of the output to be handled by a personal computer. The photoplethysmograph described in this paper is shown to be a qualitative method for assessment of changes in peripheral skin blood flow. There is potential for use of this instrument in a variety of clinical conditions.

Malate dehydrogenase from thermophilic and mesophilic bacteria. Molecular size, subunit structure, amino acid composition, immunochemical homology, and catalytic activity.

Malate dehydrogenases isolated from a number of mesophilic, moderately thermophilic, and extremely thermophilic bacteria yield upon denaturation subunits of molecular weight 32 000--36 000. Determination of their native molecular weights shows that some of the enzymes are dimeric and others are tetrameric; the two types are distributed in each of the three classes of bacteria. The amino acid compositions of the enzymes show no consistent trend that can be related to the progression of thermostability from the mesophile through the moderate thermophile to the extreme thermophile species. The tetrameric enzyme species all exhibit a high level of structural homology as judged by the criterion of immunological cross-reaction. Little cross-reaction occurs, however, between the tetramers and the dimers. The dimeric enzyme from the extreme thermophile, Thermus aquaticus, cross-reacts only weakly, if at all, even with dimeric malate dehydrogenases. The catalytic activities of the malate dehydrogenases vary over a wide range. Potassium chloride, organic solvents such as acetone, and the protein denaturants urea and guanidine hydrochloride activate a number of the malate dehydrogenases under the assay conditions employed. The diversity among the bacterial malate dehydrogenases, manifested not only in molecular size and subunit structure but also in properties such as catalytic activity and the dependence of this activity on electrolytes, organic solvents, and denaturants, indicates significant structural differences between several of these cognate enzyme species.

Cloning of the HIS3 gene of Yarrowia lipolytica.

The HIS3 gene of the yeast Yarrowia lipolytica has been cloned from a genomic library by complementation of the his3 mutation of Saccharomyces cerevisiae. The gene was subsequently subcloned in Escherichia coli and characterized by restriction enzyme mapping.

A technique for the determination of 18O/16O and 17O/16O isotopic ratios in water from small liquid and solid samples.

We have developed a new technique in which a solid reagent, cobalt(III) fluoride, is used to prepare oxygen gas for isotope ratio measurement from water derived either from direct injection or from the pyrolysis of solid samples. The technique uses continuous flow, isotope ratio monitoring, gas chromatography/mass spectrometry (irmGC/MS) to measure the delta18O and delta17O of the oxygen gas. Water from appropriate samples is evolved by a procedure of stepped pyrolysis (0-1000 degrees C, typically in 50 degrees C increments) under a flowing stream of helium carrier gas. The method has considerable advantages over others used for water analysis in that it is quick; requires only small samples, typically 1-50 mg of whole rock samples (corresponding to approximately 0.2 micromol of H2O); and the reagent is easy and safe to handle. Reproducibility in isotope ratio measurement obtained from pyrolysis of samples of a terrestrial solid standard are delta18O +/- 0.54, delta17O +/- 0.33, and delta17O +/- 0.10/1000, 1sigma in all cases. The technique was developed primarily for the analysis of meteorites, and the efficiency of the method is illustrated herein by results from water standards, solid reference materials, and a sample of the Murchison CM2 meteorite.

The formation of weathering products on the LEW 85320 ordinary chondrite: evidence from carbon and oxygen stable isotope compositions and implications for carbonates in SNC meteorites.

Isotopic analysis of nesquehonite recovered from the surface of the LEW 85320 H5 ordinary chondrite shows that the delta 13C and delta 18O values of the two generations of bicarbonate (Antarctic and Texas) are different: delta 13C = +7.9% and +4.2%; delta 18O = +17.9% and 12.1% respectively. Carbon isotopic compositions are consistent with equilibrium formation from atmospheric carbon dioxide at -2 +/- 4 degrees C (Antarctic) and +16 +/- 4 degrees C (Texas). Oxygen isotopic data imply that the water required for nesquehonite precipitation was derived from atmospheric water vapour or glacial meltwater which had locally exchanged with silicates, either in the meteorite or in underlying bedrock. Although carbonates with similar delta 13C values have been identified in the SNC meteorites EETA 79001 and Nakhla, petrographic and temperature constraints argue against their simply being terrestrial weathering products.

Purification and properties of an extracellular glucoamylase from a diastatic strain of Saccharomyces cerevisiae.

The extracellular glucoamylase from certain strains of Saccharomyces cerevisiae can be purified from culture medium by a simple chromatographic procedure. The native enzyme is heavily glycosylated and has an Mr of about 250,000, but gel filtration indicates the existence of oligomers of larger size. Dissociation yields a form of Mr about 70,000. The glucoamylase is rich in serine and threonine and in aspartic acid plus asparagine, and has a pI of 4.62 and a pH optimum of 4.5-6.5. The thermostability and resistance to denaturants of the yeast enzyme is compared with those of two other fungal glucoamylases. Kinetic data for the yeast enzyme and a variety of substrates is presented; the enzyme is particularly ineffective in cleaving alpha-(1----6)-glycosidic bonds.

Record of fluid-rock interactions on Mars from the meteorite ALH84001.

Allan Hills (ALH) 84001 is the most recently recognized member of a suite of meteorites--the SNCs--that almost certainly originated on Mars. Several factors distinguish ALH84001 from the other SNC meteorites. Preliminary studies suggest that it may be older than other martian meteorites. Moreover, it contains abundant, zoned domains of calcium-iron-magnesium carbonate that are indigenous to the sample and thus may hold important clues regarding near-surface processes on Mars and the evolution of the martian atmosphere. We report here analyses of the carbon and oxygen stable-isotope compositions of the carbonates that place constraints on their formation conditions. Our results imply the presence of at least two chemically distinct carbonates--one Ca,Fe-rich, the other Mg-rich--that are enriched in 13C relative to terrestrial carbonates (delta 13C approximately +41/1000), consistent with martian atmospheric CO2 as the carbon source. The oxygen isotope compositions of the carbonates indicate that they precipitated from a low-temperature fluid in the martian crust. Combined with textural and bulk geochemical considerations, the isotope data suggest that carbonate deposition took place in an open-system environment in which the ambient temperature fluctuated.