Audit of 26 years of obstetrics in general practice.

To assess the feasibility and quality of general practitioner obstetrics an audit of 1223 consecutive obstetric deliveries over 26 years was carried out with standard clinical records. The perinatal mortality of 9.0 per 1000 births was significantly better than the national average of about 19.0 per 1000 for the overall period. During the audit home deliveries virtually stopped. The proportion of consultant bookings and deliveries more than doubled because of more stringent booking arrangements despite relocation of the previously isolated general practitioner unit to beneath the consultant unit. Abnormal deliveries also rose significantly. A "steady state" was achieved during the final 11 years in which 73% of women booked to be delivered by their general practitioner, 64% were admitted to the general practitioner unit, and 54% were delivered by their general practitioner. Though this is enough to sustain obstetric experience, the proportion might safely be increased.     

High resolution spatio-temporal analysis of aquatic chemical signals using microelectrochemical electrodes

Detailed understanding of chemoreceptor cell transduction andfiltering depends on precise control and thus measurement ofthe chemical stimulus. In contrast to vision and hearing, accuratestimulus measurement in chemoreception has not been possibleat biologically relevant spatial and temporal scales. In thispaper we introduce a new high-speed (200 hz) electrochemicalmethod for the direct measurement of odor signals at biologicallyrelevant space scales (10-100 µm). We tested this systemin three applications: (i) temporal and spatial features ofodor plumes, (ii) stimulus calibrations in physiological recordingchambers and (iii) boundary layer diffusion measurements withinreceptor structures.     

Formation of mutagens during the frying of Hawaiian fish: correlation with creatine and creatinine content

Compounds mutagenic toward Salmonella typhimurium strain TA98 in the presence of rat-liver homogenates (S9) were formed when fish flesh was fried at 199 degrees C. Three species of Hawaiian fish commonly consumed in Hawaii (skipjack tuna, Katsuwonus pelamis; yellowfin tuna, Neothunnus macropterus; and milkfish, Chanos chanos) were cooked in an electric skillet, along with samples of sole (Microstomus pacificus). Organic extracts of the fish were tested in the Ames Salmonella mutagenic assay using tester strain TA98 and S9. Basic organic extracts of fried, but not raw, samples exhibited significant mutagenicity. The levels of mutagenicity were also higher among the red flesh Hawaiian fish ('ahi, aku and awa) than with the white flesh sole. Creatine and creatinine contents were highest in the Hawaiian fish and lower in the sole. Creatine levels in the fish were 50-100 times greater than the creatinine content and varied from a high of 645 mg/100 g wet weight of fish for yellowfin tuna to a low value of 251 mg/100 g for sole. Mutagen levels are only approximately related to creatine/creatinine levels suggesting that other components contained in these fish may be as important as the guanidines in determining the levels of mutagen in the cooked fish.     

The application of pH-sensitive spin labels to studies of surface potential and polarity of phospholipid membranes and proteins.

The effects of pH titration on the EPR spectra of imidazolidine nitroxides located at the surface of mixed bilayers composed of dimyristoylphosphatidylglycerol (DMPG) and dimyristoylphosphatidylcholine (DMPC), and at the surface of the protein, human serum albumin (HSA), have been investigated. It is found that the shift in pKa of the amino group of the imidazolidine radical from its value of 4.6 in water depends both on the interfacial polarity (delta pKapol) and on the electrostatic surface potential (delta pKael) when it is positioned at the bilayer/water interface by an anchoring hydrocarbon tail. The polarity shift is determined to be: delta pKapol = -1.3 units at the surface of DMPC bilayers at 17 degrees C, corresponding to an effective interfacial dielectric constant of epsilon approximately 37, and depends on the temperature with a coefficient of d delta pKapol/dT approximately -0.01 per degree. The electrostatic shift at the surface of DMPG bilayers is delta pKael = +1.6 units in 0.1 M KCl, which corresponds to an electrostatic surface potential of -95 mV. This electrostatic shift depends strongly both on ionic strength and on the fraction of charged lipid in the DMPC/DMPG mixtures, in a manner that agrees with the predictions of electrostatic double-layer theory. It is found that the shift in pKa of an imidazolidine radical covalently bound at the surface of HSA is determined mainly by the surface electrostatics (delta pKapol approximately 0) and corresponds to an electrostatic potential of +33 mV in 0.01 M KCl at a pH below the isoelectric point of the protein.     

Polyanion-mediated mineralization — a kinetic analysis of the calcium-carrier hypothesis in the phytoflagellatePleurochrysis carterae

Summary Polyanions are postulated intermediates in biomineralization because they sequester large numbers of calcium ions and occur in high concentrations at mineralizing foci in distantly related organisms. In this study mineral ion and polyanion metabolism was examined inPleurochrysis carterae to determine whether polyanions function as intermediate calcium-carriers during coccolith (mineralized scale) formation. In this organism mineralization occurs intracellularly in coccolith-forming saccules, and mature coccoliths are extruded through the plasma membrane into the coccosphere. The polyanions (acidic polysaccharides known as PS-1 and PS-2) are synthesized in medial Golgi cisternae and transported to the coccolith-forming saccule prior to the onset of mineral deposition; they also cover the mineral surface of mature coccoliths. Pulse-chase experiments with⁴⁵Ca²⁺ and¹⁴CO₃ ^– show the calcium uptake into the coccolith-forming saccule is much slower than carbonate uptake. The extended intracellular half-life of calcium ions destined for the coccosphere suggests that calcium is initially sequestered in more distal Golgi elements (perhaps in association with the polyanions) and enters the coccolith-forming saccule only after passage through the endomembrane system. This is consistent with previous cytochemical studies showing that the polyanions are complexed with calcium prior to mineral deposition. It has been suggested that polyanions may be degraded at the mineralization front in order to free calcium ions for precipitation with available carbonate or phosphate ions. However, this study demonstrates that the polyanions are not degraded; essentially all PS-1 and PS-2 are eventually secreted with the mineral phase into the coccosphere. The kinetics of mineral ion and polyanion secretion are consistent with a polyanion-mediated calcium transport; however, the manner in which calcium might be sequestered by and freed from the polyanions is still obscure.Abbreviations PS-1/2/3 polysaccharide 1/2/3 - EDTA ethylenediaminetetraacetic acid - TCA trichloroacetic acid     

Dynamic chain conformations in dimyristoyl glycerol-dimyristoyl phosphatidylcholine mixtures. 2H-NMR studies.

The dynamic molecular lipid chain conformations in fully hydrated dimyristoyl phosphatidylcholine (DMPC)-dimyristoyl glycerol (DMG) mixtures have been investigated by 2H-NMR spectroscopy of the individual lipid components, the sn-2 chains of which were perdeuterated or, in the case of DMG, specifically deuterated at the C-2 position. Mixtures of compositions corresponding to the three different regions of the binary phase diagram in which the fluid phase is lamellar (DMPC:DMG 70:30 mol/mol), inverted hexagonal (DMPC:DMG 45:55 and 40:60 mol/mol), or isotropic (DMPC:DMG 20:80 mol/mol) were investigated. The gel phase in all three regions of the phase diagram has a lamellar structure, with the lipid chains rotating about the molecular long axis but executing only limited angular excursions. In the fluid lamellar phase of the 70:30 mol/mol DMPC-DMG mixture the profile of segmental chain flexibility is similar to that in single-component phospholipid bilayers and is characterized by an order parameter plateau for both lipid components. The chain order of the DMPC component is greater than in bilayers of DMPC alone and is also greater than that of the DMG component. In the inverted hexagonal phase of the 45:55 mol/mol DMPC-DMG mixture the chain flexibility profile is characterized by more widely spaced segmental order parameters off the plateau region. The intrinsic degree of chain order in the inverted hexagonal phase is less than in the lamellar phase of the 70:30 mol/mol mixture, and the difference in chain order between the DMPC and DMG components is reduced relative to that in the lamellar phase. The unique conformational features at the C-2 position of the sn-2 chain that characterize bilayers of diacyl phospholipids are found also for the diacylglycerol molecules in the fluid lamellar phase and most probably also in the inverted hexagonal phase. The DMG molecules are therefore integrated in the membrane (or nonlamellar lipid phase) in a configuration that is similar to that of the phospholipids and different from the crystal structure of diacylglycerols.     

Differential scanning calorimetry of thermotropic phase transitions in vitaminylated lipids: aqueous dispersions of N-biotinyl phosphatidylethanolamines.

The thermotropic phase behavior of a homologous series of saturated diacyl phosphatidylethanolamines in which the headgroup is N-derivatized with biotin has been investigated by differential scanning calorimetry. In 1 M NaCl, derivatives with acyl chainlengths from C(12:0) to C(20:0) all exhibit sharp chain-melting phase transitions, which are reversible with a hysteresis of 1.5 degrees or less, except for the C(12:0) lipid which has a transition temperature below 0 degree C. The transition enthalpy and the transition entropy depend approximately linearly on the lipid chainlength, with incremental values per CH2 group that are very similar to those obtained for the corresponding underivatized phosphatidylethanolamines in aqueous dispersion. The chainlength-independent contribution to the transition enthalpy is significantly smaller than that for the underivatized phosphatidylethanolamines, and that for the transition entropy is much smaller; the latter suggesting that the N-biotinylated phosphatidylethanolamine headgroups are differently hydrated from those of the underivatized lipids. The gel-to-fluid phase transition temperatures of the N-biotinylated lipids are lower than those of the parent phosphatidylethanolamines, and their chainlength dependence conforms well with that predicted by assuming that the transition enthalpy and entropy are linearly dependent on chainlength. Although the chain-melting phase behavior is generally similar to that of the parent phosphatidylethanolamines, the gel phases (and the fluid phases in the case of chainlengths C(12:0) to C(16:0)) have a different lyotropic structure in the two cases, and this is reflected in the chainlength-independent contributions to the thermodynamic parameters. In the absence of salt, the thermotropic phase behavior of aqueous dispersions of the N-biotinyl phosphatidylethanolamines is considerably more complex.(ABSTRACT TRUNCATED AT 250 WORDS)     

Linkage analysis of sex determination in the honey bee (Apis mellifera)

A colony-level phenotype was used to map the major sex determination locus (designatedX) in the honey bee (Apis mellifera). Individual queen bees (reproductive females) were mated to single drones (fertile males) by instrumental insemination. Haploid drone progeny of an F1 queen were each backcrossed to daughter queens from one of the parental lines. Ninety-eight of the resulting colonies containing backcross progeny were evaluated for the trait low brood-viability resulting from the production of diploid drones that were homozygous atX. DNA samples from the haploid drone fathers of these colonies were used individually in polymerase chain reactions (PCR) with 10-base primers. These reactions generated random amplified polymorphic DNA (RAPD) markers that were analyzed for cosegregation with the colony-level phenotype. One RAPD marker allele was shared by 22 of 25 drones that fathered low brood-viability colonies. The RAPD marker fragment was cloned and partially sequenced. Two primers were designed that define a sequence-tagged site (STS) for this locus. The primers amplified DNA marker fragments that cosegregated with the original RAPD marker. In order to more precisely estimate the linkage betweenX and the STS locus, another group of bees consisting of progeny from one of the low-brood viability colonies was used in segregation analysis. Four diploid drones and 181 of their diploid sisters (workers, nonfertile females) were tested for segregation of the RAPD and STS markers. The cosegregating RAPD and STS markers were codominant due to the occurrence of fragment-length alleles. The four diploid drones were homozygous for these markers but only three of the 181 workers were homozygotes (recombinants). Therefore the distance betweenX and the STS locus was estimated at 1.6 cM. An additional linked marker was found that was 6.6 cM from the STS locus.