Polymorphic phases of galactocerebrosides: spectroscopic evidence of lamellar crystalline structures

Fourier transform infrared spectroscopy was applied to study the structural and thermal properties of bovine brain galactocerebroside (GalCer) containing amide linked non-hydroxylated or alpha-hydroxy fatty acids (NFA- and HFA-GalCer, respectively). Over the temperature range 0-90 degrees C, both GalCer displayed complex thermal transitions, characteristic of polymorphic phase behavior. Upon heating, aqueous dispersions of NFA- and HFA-GalCer exhibited high order-disorder transition temperatures near 80 and 72 degrees C, respectively. En route to the chain melting transition, the patterns of the amide I band of NFA-GalCer were indicative of two different lamellar crystalline phases, whereas those of HFA-GalCer were suggestive of lamellar gel and crystalline bilayers. Cooling from the liquid-crystalline phase resulted in the formation of another crystalline phase of NFA-GalCer and a gel phase of HFA-GalCer, with a phase transition near 62 and 66 degrees C, respectively. Prolonged incubation of GalCer bilayers at 38 degrees C revealed conversions among lamellar crystalline phases (NFA-GalCer) or between lamellar gel and crystalline bilayer structures (HFA-GalCer). Spectral changes indicated that the temperature and/or time induced formation of the lamellar crystalline structures of NFA- and HFA-GalCer was accompanied by partial dehydration and by rearrangements of the hydrogen bonding network and bilayer packing mode of GalCer.

[Quality and improvement propositions for the Annecy emergency medical services]

Emergency visits are one of the most common ways patients are admitted to hospitals. This study aims to characterise emergency visits in the Annecy District, in order to identify future actions for better management. Four studies were implemented: telephone surveys among 600 households and 130 physicians; and two observational studies of emergency visits to 80 physicians and to hospital emergency services. We observed that the hospital emergency service offers patients a good service, and therefore attracts many minor pathologies not requiring a hospital visit. Implementation of alternative structures, outside the hospital, to offer similar service must be considered. Co-operation among the different actors must be improved, and can benefit from new communication technology.

A Fourier-transform infrared study of the interaction between germ-cell specific sulfogalactosylglycerolipid and dimyristoylglycerophosphocholine

In this study, we investigated structural and dynamic changes of sulfogalactosylglycerolipid (SGG) and dimyristoylglycerophosphocholine (DMPC) in a liposomal system (SGG+DMPC, molar ratio 2:3) by Fourier-transform infrared (FTIR) spectroscopy. Cooling of the preheated SGG liposomes (5-65 degrees C) revealed that the liquid crystalline-to-gel phase transition was centered at 45 degrees C. SGG+DMPC liposomes showed a single phase transition at 28 degrees C. Spectral changes of the ester C&z. dbnd6;O groups of SGG and DMPC in the mixed liposomes indicated a decrease in their interfacial hydrogen bonding intermolecularly and with water. Analysis of SGG's symmetric and antisymmetric CH(2) stretching bands revealed that the insertion of DMPC into SGG bilayers increased the number of gauche conformers in SGG's hydrocarbon chains. Overall, the SGG+DMPC liposomes were homogeneous, with reduced interfacial hydrogen bonding and increased orientational and conformational disorder of SGG's hydrocarbon chains.

FTIR study of the monosialoganglioside GM1 in perdeuterated dimyristoylglycerophosphocholine (DMPCd54) multilamellar bilayers: spectroscopic evidence of a significant interaction between Ca2+ ions and the sialic acid moiety of GM1

Fourier transform infrared (FTIR) spectroscopy was employed to study bovine brain GM1 and perdeuterated dimyristoylglycerophosphocholine (DMPCd54) multilamellar dispersions (mole fractions of GM1 in DMPCd54: 0.12, 0.15, 0.19, 0.26, 0.34, 0.41, and 0.58), in the absence and presence of 10 mM CaCl2. GM1 micelles did not display a thermal phase transition in the temperature range 5-60 degrees C. Moreover, the ceramide moiety of GM1 inserted into the hydrophobic core of DMPCd54 bilayers and was capable of undergoing a single, cooperative phase transition (Tm = 22-28 degrees C, depending on GM1 content) in a bilayer system. This suggested that the mixed bilayers consisted of a homogeneous mixture and that GM1 was uniformly dispersed in the bilayer plane rather than segregated into regions of relative enrichment. The coexistence of GM1 and DMPCd54 in a bilayer environment induced a rearrangement of the interfacial hydrogen bonding network of the amide I and ester C=O groups, relative to GM1 micelles and DMPCd54 bilayers, respectively. The modifications induced by GM1 might ultimately modulate surface events such as lipid-lipid and/or lipid-protein interactions. The spectroscopic results also suggested that the glycolipid's headgroup surface location and conformation in bilayers allow GM1 to act as a receptor for Ca2+ via its sialic acid moiety.

Interaction between sulfogalactosylceramide and dimyristoylphosphatidylcholine increases the orientational fluctuation of their lipid hydrocarbon chains

The objective of this study was to investigate the interaction between sulfogalactosylceramide (SGC) and dimyristoylphosphatidylcholine (DMPC) in a mixed model liposomal system (molar ratio SGC:DMPC, 2:3). Structural and dynamic changes of the liposome components were monitored by Fourier-transform infrared spectroscopy (FTIR). Thermotropic FTIR analysis of the mixed liposomes showed a single gel/liquid crystalline phase transition, centered at approximately 42 degrees C. Spectral changes of the amide and ester C = O bands arising from functional groups at the interfacial region indicated a reduced hydrogen bonding of these groups in the mixed liposomes. Pressure-tuning FTIR of mixed liposomes showed that the methylene chains of SGC and DMPC were more orientationally disordered than those of the individual lipid SGC liposomes or DMPC liposomes. These results suggest that the mixed liposomes (molar ratio SGC:DMPC, 2:3) consisted of a homogeneous mixture of SGC and DMPC molecules in which mutual shielding reduced hydrogen bonding in the interfacial region, with a concurrent increase in the orientational disorder of the hydrocarbon chains of both SGC and DMPC.

Modulation of phospholipase A2 activity by aminoglycosides and daptomycin: a Fourier transform infrared spectroscopic study

The antibiotics known as aminoglycosides are commonly used to treat severe infections caused by Gram-negative bacteria. Unfortunately, they often lead to acute renal failure after their accumulation in the lysosomes of renal cells, where an inhibition of the phospholipid catabolism is observed. The lipopeptidic antibiotic daptomycin has been shown to reduce the nephrotoxicity of aminoglycosides, but the exact mechanism of this protection is still unknown. In the present study, Fourier transform infrared spectroscopy (FTIR) has been used to monitor the hydrolysis of phosphatidylcholine by phospholipase A2 (PLA2) from Naja mocambique mocambique venom in the presence of various aminoglycosides and/or daptomycin. Gentamicin and amikacin inhibited the reaction in its early stage. Kanamycin A, tobramycin, and especially kanamycin B enhanced the initial enzyme activity by reducing the lag time. After the initiation period, the reaction proceeded at a much slower rate in the presence of gentamicin. On the other hand, daptomycin led to dramatic alterations of the hydrolysis profile: the initial latency period was eliminated, and the maximal extent of hydrolysis was reduced. When both daptomycin and any of the aminoglycosides were present, the latency period also disappeared, and the phospholipase activity was higher than with the lipopeptide alone. The most drastic change occurred with gentamicin, which was the most inhibitory aminoglycoside when used alone but worked synergistically with daptomycin to yield the most dramatic activation of PLA2.

UCH operations improvement: emergency department benchmarking project summary

The editors are providing this Executive Summary by the University HealthSystem Consortium of their Emergency Department Benchmarking Project. The report has been reviewed by the participating members listed at the end of the summary. The summary report provides both an interesting account of how a benchmarking project of considerable magnitude can be accomplished but also indicates how important comparative data can be used to improve individual programs.

Comparison of the effects of amikacin and kanamycins A and B on dimyristoylphosphatidylglycerol bilayers. An infrared spectroscopic investigation

Aminoglycoside antibiotics are very effective against severe Gram-negative infections, but their clinical use is associated with nephrotoxic side-effects. The cascade of events leading to acute renal failure involves an impairment of lysosomal phospholipase activity, which is thought to result from the direct interaction of the drugs with the head group of negative phospholipids. Fourier transform infrared spectroscopy was used to study the effects of three aminoglycosides from the kanamycin family (amikacin and kanamycins A and B) on dimyristoylphosphatidylglycerol (DMPG) bilayers at lysosomal pH. The results obtained were consistent with a tightening of the lipidic network caused by the neutralization of the negative head groups of DMPG by the positive charges of the aminoglycosides. These antibiotics induced an increase of the transition temperature of DMPG, a decrease of both the frequency and relative intensity of the hydrogen-bonded carbonyl component, and a decrease of the phosphate antisymmetric band frequency. Kanamycin B, which is known to be the most nephrotoxic drug of the three, exhibited the greatest effects on the transition temperature and on the carbonyl stretching band. A comparison of the nature and extent of the spectral changes led us to conclude that amikacin lies flat on the bilayer surface, whereas kanamycin B is located between the lipidic head groups and quite close to some of the carbonyl groups. Finally, a possible correlation between the importance of bilayers perturbation and the respective inhibitory potency against phospholipases was examined.

Choristomas of the seventh and eighth cranial nerves

Choristomas, masses of normal tissues in aberrant locations, contain smooth muscle fibers and fibrous tissues. We describe the MR imaging features of two choristomas located in the internal auditory canals and arising from the facial and vestibulocochlear nerves. Both lesions enhanced with contrast material. In one case, enhancement was seen in the geniculate ganglion and greater superficial petrosal nerve. In the other, a medial component enhanced less than the lateral component did.

Seasonal mood disturbances in collegiate hockey players

OBJECTIVE

THE PURPOSE OF THIS PAPER IS TO: 1) describe the seasonal affective disorder syndrome using a case illustration, 2) provide a simple and reliable method for identifying seasonal affective disorder, and 3) provide data as to the prevalence of the syndrome in a subset of collegiate hockey players.

DESIGN AND SETTING

Collegiate hockey players were selected, because their practices begin in the fall and play is completed in the spring. The teams selected for participation were from the far Northwest and the upper Midwest regions.

SUBJECTS

Sixty-eight Division I hockey players volunteered for the study. The three teams from which the subjects were chosen were located above latitude 42 degrees /45' north. Subjects were from the northern latitudes.

MEASUREMENTS

The Seasonal Pattern Assessment Questionnaire was used to screen for seasonality. A sample of the athletes was also examined using the Hamilton Rating Scale for Depression together with the Diagnostic and Statistical Manual of Mental Disorders (4th ed) criteria for Seasonal Pattern Specifier.

RESULTS

Thirty-three (51%) were asymptomatic, 7 (11%) met the criteria for seasonal affective disorder, and 25 (39%) hockey players scored in the range that could classify them as candidates for subsyndromal seasonal affective disorder.

CONCLUSIONS

The prevalence of seasonal affective disorder among our sample approximated the national norm for the northern latitudes. However, the prevalence of subsyndromal seasonal affective disorder in our population was 25% compared to 13% reported nationally. Light therapy has been shown to reverse the effects of the disorders; however, further research needs to be conducted to determine its acceptance and effectiveness by the athletic population.

MRI and clinical decisions in cochlear implantation

High-resolution computed tomography (HRCT) is the standard imaging technique used in cochlear implantation. However, cochlear and retrocochlear soft-tissue abnormalities may not be detected with HRCT alone. To determine whether magnetic resonance imaging (MRI) provides clinically significant information in addition to HRCT in the evaluation of candidates for cochlear implants, we performed a prospective study of 13 consecutive patients with cochlear implant patients receiving preoperative, high-resolution fast spin-echo T2-weighted MRI scans of the temporal bone. MRI identified unanticipated cochlear fibrosis in one patient, vestibular schwannoma in one patient, patency in the second turn of the cochlea in a patient with labyrinthitis ossificans, and disproved cochlear fibrosis suspected on HRCT imaging in one patient. These findings were significant for clinical decisions regarding candidacy for surgery, side selection for surgery, and surgical technique in cochlear implantation. Our experience suggests a high-resolution T2-weighted MRI of the temporal bone should be used preoperatively in addition to HRCT before cochlear implantation.

Molecular basis of the inhibition of gentamicin nephrotoxicity by daptomycin; an infrared spectroscopic investigation

The lipopeptide daptomycin has been reported to reduce in vivo the nephrotoxicity of aminoglycoside antibiotics (Wood et al. (1989) Antimicrob. Agents Chemother. 33, 1280-1285; Beauchamp et al. (1990) Antimicrob. Agents Chemother. 34, 139-147). A recent dialysis study confirmed the existence of an electrostatic interaction between daptomycin and tobramycin (Couture et al. (1994) Antimicrob. Agents Chemother. 38, 742-749). The interaction of gentamicin with daptomycin and phosphatidylinositol (PI) dispersions was investigated by FTIR spectroscopy. We found no evidence of a direct interaction involving the neutralization of the aspartate groups of daptomycin by gentamicin and the amide I band of daptomycin did not reveal significant conformational changes of its peptidic moiety. On the other hand, daptomycin readily inserts within bilayers of PI, dimyristoylphosphatidylglycerol or dipalmitoylphosphatidylcholine, as judged from its influence on the fluidity of these bilayers. The incorporation of daptomycin into PI bilayers has no significant effect on the lipopeptide amide I band. Gentamicin also binds to PI bilayers and the associated modifications of the lipid bands are consistent with a tightening of the lipid network resulting from head group neutralization by gentamicin. The affinity of the aminoglycoside for PI is slightly increased in the presence of daptomycin, in agreement with the results of the dialysis study mentioned above. The lipid features indicate that its head group is still affected by gentamicin charges, but the thermotropic behavior of the hydrophobic portion becomes similar to that of the pure lipid. It is proposed that the contribution of daptomycin to the membrane charge density and its effect on the lipid packing both combine to counteract the inhibition of phospholipase activity due to aminoglycosides. Further work will attempt to determine how the peptide rings and gentamicin molecules are organized at the bilayer surface, how specific these interactions are and to confirm the influence of daptomycin on the phospholipid catabolism.

False-Positive Magnetic Resonance Imaging of Small Internal Auditory Canal Tumors: A Clinical Radiologic, and Pathologic Correlation Study

Magnetic resonance imaging with gadolinium facilitates the early diagnosis of internal auditory canal tumors at a small enough stage to permit increasing application of hearing preservation surgical techniques. Surgeons report successful removal of tumors as small as 3 mm, which are diagnosed with enhanced magnetic resonance imaging. A retrospective study was performed to determine the risk of false-positive “tumor” diagnosis with enhanced magnetic resonance imaging. We reviewed the imaging records, office notes, and surgical records of 112 consecutive “tumors” involving the internal auditory canal treated by the Wilford Hall USAF Medical Center Neurotology Service between July 1991 and July 1994. Two categories of false-positive magnetic resonance imaging were Identified: (1) surgically confirmed absence of internal auditory canal neoplasm and (2) spontaneous resolution of the internal auditory canal lesions on subsequent, enhanced magnetic resonance images. Overall, eight false-positive scans were identified. Three were surgically confirmed as false-positive, and five resolved on subsequent Imaging studies. All cases were smaller than 6 mm and involved the distal internal auditory canal (fundus). The surgically confirmed cases were approached through a middle fossa technique with successful hearing preservation. The overall rate of surgical false-positive results was 3.5% (3 cases in 86 surgeries). However, the overall false-positive rate for intracanalicular “tumors” was 32% (8 cases in 25 intracanalicular lesions). Although hearing preservation is more likely in small lesions, the surgeon must consider the possibility that an internal auditory canal lesion smaller than 6 mm may actually represent a nonneoplastic process. Enhancing lesions limited to the internal auditory canal fundus may be treated by reimaging the patient in 6 months after the first image rather than by prompt surgical exploration.

Daptomycin may attenuate experimental tobramycin nephrotoxicity by electrostatic complexation to tobramycin

The lipopeptidic antibiotic daptomycin is reported to reduce experimental tobramycin nephrotoxicity (D. Beauchamp, M. Pellerin, P. Gourde, M. Pettigrew and M. G. Bergeron, Antimicrob. Agents Chemother. 34:139-147, 1990; C. A. Wood, H. C. Finkbeiner, S. J. Kohlhepp, P. W. Kohnen, and D. C. Gilbert, Antimicrob. Agents Chemother. 33:1280-1285, 1989). In an attempt to explain these results, the in vivo and in vitro interactions between daptomycin and tobramycin were studied. Tobramycin alone and preincubated with negatively charged phospholipid bilayers (liposomes) was dialyzed against increasing concentrations of daptomycin in buffer at pH 5.4. A significant drop in the concentration of tobramycin was observed when daptomycin was added to the opposite half cells. Furthermore, daptomycin induced a concentration-dependent release of lipid-bound tobramycin. Gold labeling experiments showed that daptomycin could be incorporated into phospholipid layers. Female Sprague-Dawley rats were treated with daptomycin alone, with tobramycin alone, or with the combination over 2 to 10 days. Levels of daptomycin and tobramycin in serum were similar in all groups. The levels of tobramycin in the renal cortex increased significantly with time and, on day 10, reached values of 654 +/- 122 and 844 +/- 298 micrograms/g of tissue (mean +/- standard deviation; not significant) in animals treated with tobramycin and the combination of daptomycin-tobramycin, respectively. No significant difference was observed in the levels of tobramycin in the kidneys between animals treated with tobramycin or the daptomycin-tobramycin combination at any time. By contrast, daptomycin levels were significantly higher in the renal cortexes of animals treated with daptomycin-tobramycin in comparison with those in the renal cortexes of animals treated with daptomycin alone on days 6,8, and 10 (P < 0.01). For immunogold labeling studies, animals were killed 4 h after a single injection of daptomycin alone or daptomycin in combination with tobramycin. Daptomycin was found throughout the matrixes of the lysosomes of proximal tubular cells of animals treated with daptomycin alone. In animals treated with the combination of daptomycin and tobramycin, daptomycin was associated with intralysosomal myeloid bodies. Our results suggest that daptomycin might attenuate experimental aminoglycoside nephrotoxicity by interacting with the aminoglycoside, perhaps electrostatically, and thereby protecting intracellular targets of toxicity.

Interactions of aminoglycoside antibiotics with phospholipids. A deuterium nuclear magnetic resonance study

The effect of several aminoglycoside (AG) antibiotics on aqueous multilamellar dispersions of mixtures of phosphatidylinositol (PI) and deuterated phosphatidylcholine (PC) has been studied by deuterium (2H) NMR. Isepamicin and amikacin gave rise to no significant changes in 2H-NMR lineshape relative to that of the lipid mixture without antibiotic. Both kanamycin A and B, which have a greater affinity for PI than the other two antibiotics examined in this study, induced temperature-dependent changes in 2H-NMR lineshapes and associated spectral moments. The results are consistent with an antibiotic-induced lateral phase separation giving rise to PC-enriched domains free of drug and PI-AG domains. These effects are correlated with the inhibitory potency of aminoglycosides towards PC degradation.

Efficacy of moxidectin against naturally acquired nematode infections in cattle

The efficacy of moxidectin, a new endectocide against natural nematode infections, was evaluated. Twenty-five calves were divided into two groups of eight calves each and a third group of nine calves. Moxidectin was administered s.c. to two groups (I, 0.2 mg kg-1 body weight (BW); II, 0.3 mg kg-1 BW) and the third group (III) received the vehicle (placebo) s.c. Two pre-treatment and one post-treatment faecal nematode egg count determinations were made from all calves, and they were necropsied 2 weeks after treatment for the identification and enumeration of nematode parasites. Group III calves, which received the drug-free vehicle, harboured eight species of nematodes (Ostertagia ostertagi, Trichostrongylus axei, Cooperia oncophora, Cooperia punctata, Nematodirus helvetianus, Trichuris discolor, Oesophagostomum radiatum and Dictyocaulus viviparus). The mean total worm burden for this group was 8935. There was a significant reduction in the numbers of many species of nematodes (Ostertagia, Trichostrongylus, Cooperia and Nematodirus) in both treated groups. Cooperia oncophora was reduced by 94% in Group I and by 96% in Group II, while all other nematode species were reduced by 99%. Immature stages of Ostertagia and Nematodirus were significantly reduced in the two treated groups. Two weeks after treatment, the mean faecal egg counts of both treated groups were reduced by more than 98%. There was no significant difference in mean total worm burdens or egg counts between the two treated groups.

Apamin, a highly potent blocker of the TTX- and Mn2(+)-insensitive fast transient Na+ current in young embryonic heart

The whole-cell current clamp and voltage clamp techniques were used to record the slow Na+ action potentials (APs) and the inward current in cultured single ventricular cells isolated from young (3 day-old) embryonic chicks. The slow Na+ APs had a +Vmax of 21.5 +/- 7.5 V/s (in 10 different single cells) and the macroscopic inward current responsible for the rising phase of these APs was a fast transient (ft) current. The ft inward current was sensitive to changes in [Na]o but not to changes in [Ca]o. This channel was found to be permeable to Li+ and Ba2+. Analysis of Na+ current decay suggests a second-order process of current decay. The slow Na+ APs and the ft inward current were insensitive to tetrodotoxin (TTX) and Mn2+. This current was also insensitive to the inorganic Ca2+ blockers, Ni2+, Cd2+ and La3+. At low concentration (10(-9)-10(-6) M) the organic Ca2+ blockers, (-)D888 and nifedipine had no effect on the TTX- and Mn2(+)-insensitive INa. However, at a high concentration (10(-5) M), the Ca2+ blockers, (-)D888 and nifedipine, completely blocked the slow Na+ APs and the TTX- and Mn2(+)-insensitive ft inward Na+ current responsible for the rising phase of the APs. High concentration of verapamil (10(-5) M) and D-600 (10(-5) M) had little depressant effects due to their frequency dependence. Apamin, a toxin in the bee venom, that was previously reported by our group to block the slow Ca2+ APs (Bkaily et al., 1985) and the slow Ca2+ current (Bkaily et al., 1988b), greatly decreased the TTX- and Mn2(+)-insensitive ft INa at 10(-10) M. Thus, the inward current responsible for the rising phase of the slow Na+ APs in 3 day-old embryonic chick heart shows fast transient activation and is TTX- and Mn2(+)-insensitive. This channel is highly sensitive to apamin and shares few characteristics with the Ca2+ channel and the TTX-sensitive fast Na+ channel.

Activity of the hypaxial muscles during walking in the lizard Iguana iguana

The role that the hypaxial muscles play in locomotion has been largely ignored by biologists. In tetrapods, there are at least three possibilities. First, the hypaxial muscles might bend the trunk laterally to increase stride length. Second, they might stabilize the trunk against the horizontal, lateral and vertical components of the propulsive force. Alternatively, they might not be involved in locomotion. This study evaluated these three hypotheses by analyzing the activity of the hypaxial muscles of green iguanas (Iguana iguana). During walking, the rectus abdominis, obliquus externus superficialis and profundus, intercostales externi, and ventral portion of the intercostales interni on one side of the trunk acted synergistically with the lateral portion of the intercostales interni and obliquus internus on the other side of the trunk. This pattern supports the hypothesis that the hypaxial muscles act to stabilize the trunk during locomotion. Specifically, the longitudinally oriented rectus abdominis, obliquus externus profundus and ventral portion of the intercostales interni appear to stabilize the trunk against the horizontal and lateral components of the propulsive force, which tend to rotate the girdles in the horizontal plane. The obliquely oriented obliquus externus superficialis, intercostales externi, lateral portion of the intercostales interni and obliquus internus appear to stabilize the trunk against the vertical component, which induces long-axis torsion in the trunk. Thus, the demands of locomotion may provide a functional explanation for the basic organization of the hypaxial muscles of tetrapods.

Pressure effects on sarcoplasmic reticulum: a Fourier transform infrared spectroscopic study

The Ca2(+)-ATPase of sarcoplasmic reticulum is irreversibly inactivated by exposure to 1.5-2.0 kbar pressure for 30-60 min in a Ca2(+)-free medium; mono- or decavanadate (5 mM) or to a lesser extent Ca2+ (2-20 mM) protect against inactivation (Varga et al. (1986) J. Biol. Chem. 261, 13943-13956). The structural basis of these effects was analyzed by FTIR spectroscopy of sarcoplasmic reticulum in 2H2O medium. The inactivation of the Ca2(+)-ATPase at 1.5-2.0 kbar pressure in a Ca2(+)-free medium was accompanied by changes in the Amide II region of the spectrum (1550 cm-1), that are consistent with increased hydrogen-deuterium (H-2H) exchange, and by the enhancement of a band at 1630 cm-1 in the Amide I region, that is attributed to an increase in beta sheet. The frequency of the peak of the Amide I band shifted from about 1648 cm-1 at atmospheric pressure to 1642 cm-1 at approximately equal to 12.5 kbar pressure, suggesting a decrease in alpha helix, and an increase in beta and/or random coil structures. Upon releasing the pressure, the shift of the Amide I band was partially reversed. Vanadate (5 mM), and to a lesser extent Ca2+ (2-20 mM), protected the Ca2(+)-ATPase against pressure-induced changes both in the Amide I and Amide II regions of the spectrum, together with protection of ATPase activity. These observations establish a correlation between the conformation of the Ca2(+)-ATPase and its sensitivity to pressure. The involvement of the ATP binding domain of the Ca2(+)-ATPase in the pressure-induced structural changes is suggested by the decreased polarization of fluorescence of fluorescein 5'-isothiocyanate covalently attached to the enzyme.

Protective effect of lipidic surfaces against pressure-induced conformational changes of poly(L-lysine)

Poly(L-lysine) bound to phosphatidylglycerol or phosphatidic acid bilayers was submitted to hydrostatic pressure in a diamond anvil cell to investigate whether the lipidic surfaces can protect the polypeptide against pressure-induced conformational transformations. The amide I region of the infrared spectrum of dimyristoylphosphatidic acid bound polylysine shows that most of the polypeptide retains its beta-sheet structure up to 19 kbar, while it is known to convert entirely to alpha-helix at approximately 2 kbar in the absence of the lipid [Carrier, D., Mantsch, H.H., & Wong, P.T.T. (1989) Biopolymers (in press)]. The simultaneous binding of the polypeptidic molecules to two opposing bilayers appears to be required in order to preserve the beta-sheet structure at pressures over approximately 9 kbar: a small proportion of the polypeptide, most likely the molecules at the surface of the aggregated bilayers, was found to convert to unordered and eventually to alpha-helical conformations in the pressure range 9-19 kbar. The decrease from 1612 to 1606 cm-1 of the frequency of the major beta-sheet component of the infrared amide I band as the pressure is raised to 6 kbar indicates a strengthening of the interchain hydrogen bonds. The high-pressure infrared spectra of polylysine bound to dimyristoyl- and dipalmitoylphosphatidylglycerol show that the polypeptide remains alpha-helical up to approximately 12 kbar, though the changes in the bandshape indicate an increase in hydrogen bond strength. The formation of a small amount of beta-sheet was observed during decompression and is attributed to the effect of dehydration on the polypeptidic molecules located at the surface of the aggregates.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamics and orientation of glycolipid headgroups by 2H-NMR: gentiobiose

Deuterium nuclear magnetic resonance has been used to investigate the dynamics and determine the orientation of the headgroup of the glycolipid 1,2-di-O-tetradecyl-3-O-(6-O-beta-D-glucopyranosyl-beta-D-glucopyranosyl )-sn- glycerol (beta-DTDGL), in aqueous multilamellar dispersions. In addition, its anomeric analog, having an alpha glucose-glycerol linkage, was prepared and examined. The lipids were labelled with deuterium at specific positions in the disaccharide moiety. Analysis of the deuterium quadrupolar splittings for the first glucose ring (glycerol-linked) gave segmental order parameters of 0.43 and 0.35 for the beta and alpha isomers, respectively. Both isomers had similar orientations of the sugar ring relative to the bilayer surface, as determined for lipid in the liquid-crystalline phase. 2H-NMR results for the lipid labelled at C-6' are consistent with a single conformation about the C-5'-C-6' bond of the first glucose residue, with a dihedral angle (O-5'-C-5'-C-6'-O-6') of -17 degrees. The results obtained for the second sugar ring suggest that two conformers may be present, which are in slow exchange on the 2H-NMR timescale. Measurements of longitudinal relaxation times, T1z, gave similar values for both sugar moieties in the headgroup, suggesting that the disaccharide does not exhibit the flexibility expected about the 1----6 linkage. Since T1z for 2H in these compounds decreases with increasing temperature and increases with magnetic field strength, the motion(s) dominating relaxation is in the long-correlation-time regime [omega 0 tau c)2 greater than 1). Thus, the gentiobiosyl headgroup undergoes the slowest motion of the glycolipid headgroups studied to date.

Study of the effect of poly(L-lysine) on phosphatidic acid and phosphatidylcholine/phosphatidic acid bilayers by raman spectroscopy

The effect of polylysine (PLL) on dimyristoylphosphatidic acid (DMPA), on dimyristoyl-phosphatidylcholine (DMPC), and on mixtures of these lipids was investigated by Raman spectroscopy. These results show that long polylysine (Mr approximately 200,000) increases the stability of the acyl chain matrix of DMPA to form a more closely packed structure with a stoichiometry of one lysine residue per PA molecule. On the other hand, short PLL (Mr 4000) destabilizes the PA bilayer, and the complex formed undergoes a gel to liquid-crystalline transition at a lower temperature than of the pure lipid. For both cases, we have observed that bound polylysine adopts a beta-sheet conformation as opposed to the alpha-helical structure previously found for dipalmitoylphosphatidylglycerol/long PLL complexes [Carrier, D., & Pézolet, M. (1984) Biophys. J. 46, 497-506]. The difference in the thermal behavior of complexes of DMPA with long and short polylysines is believed to be associated with the fact that in the complex the long polypeptide adopts the beta-sheet conformation over the whole range of temperatures investigated while the short one undergoes a change of conformation from beta-sheet of random coil upon heating. Therefore, the conformation of the lipid-bound polypeptides depends on the nature of the polar head group of the lipid, not only on its net charge, and it affects considerably the thermotropism of the lipid. On the other hand, both long and short polylysines show no affinity for phosphatidylcholine since the temperature profiles of DMPC and of DMPC/PLL complexes exhibit exactly the same behavior.(ABSTRACT TRUNCATED AT 250 WORDS)

Investigation of polylysine-dipalmitoylphosphatidylglycerol interactions in model membranes

The effect of poly(L-lysine) on dipalmitoylphosphatidylglycerol bilayers has been studied by Raman and infrared spectroscopies, small-angle X-ray diffraction, and carboxyfluorescein escape experiments. The polypeptide is shown to induce a stabilization of the bilayer detected by the increase of interchain vibrational coupling and a slight decrease of the overall disorder. In addition, long polylysine (Mr 150,000) induces a positive shift of the gel to fluid transition temperature and, at lipid to lysine molar ratios greater than 1, a lateral phase separation within the bilayer. Raman and infrared spectra indicate modifications at the head group level. In contrast, short polylysine (Mr 4,000) leads to a decrease of the lipid thermotropic transition temperature, and no modification of the polar head group and no phase separation could be observed. These differences between short and long polypeptides are correlated with the conformation the polypeptide adopts upon binding to the lipid, which favors the formation of alpha-helices in the case of long polypeptides (Mr greater than or equal to 14,000). The X-ray data suggest that the basic polypeptide acts as a bridge between neighboring bilayers, thus causing their aggregation and dehydration.

[Valve replacement associated with aorto-coronary bypass in ischemic mitral insufficiency]

26 cases of ischaemic mitral regurgitation (MR) were treated by combined surgery: mitral valve replacement (MVR) and coronary bypass grafting (CBG). This type of operation is not common (1.3 p. 100 of all operations) and is usually reserved for men (21 cases) of middle age (average 59 years). A half of the cases had suffered previous myocardial infarction (MI), an average 5 months before surgery (range 20 days to 2 years). The other half had severe angina or ECG changes of myocardial ischaemia. 23 patients were in Class IV (15 patients) or Class III (8 patients) of the NYHA classification. 6 of the cases required intraaortic balloon pumping. Mitral regurgitation was severe () in half of the cases with a raised pulmonary capillary (mean V wave = 52 mmHg) and systolic pulmonary artery pressures (mean = 47 mmHg: exceeding 60 mmHg in 7 cases). The coronary lesions were severe in 18 patients (12 cases of double and 6 of triple vessel disease including 2 cases of left main stem stenosis). Ruptured chordae were found in 11 cases and papillary muscle necrosis in 4 cases. Surgery comprised MVR with 12 bioprostheses and 14 mechanical prostheses. 33 CBG were performed (anterior wall: 15 cases, posterior wall: 11 cases). In addition, one tricuspid annuloplasty and 3 ventricular aneurysmectomies were carried out. The hospital mortality was 15.4 p. 100. The main causes of morbidity were low output states and postoperative MI (2 cases).(ABSTRACT TRUNCATED AT 250 WORDS)

Raman spectroscopic study of the interaction of poly-L-lysine with dipalmitoylphosphatidylglycerol bilayers

The interaction of the basic polypeptide poly-L-lysine with the negatively charged phospholipid dipalmitoylphosphatidylglycerol was studied using Raman spectroscopy. The nature of the interaction appeared to depend on the molar ratio of the constituents. At up to one lysine group per lipid molecule, the bilayer was stabilized by the polypeptide that underwent a conformational transition toward an ordered alpha-helical structure, in which the electrostatic interactions were probably maximal. The stabilization of the bilayer was detected by an increase in both the temperature of the thermotropic transition of the lipid and the interchain vibrational coupling of the methylene C-H vibrations. At higher poly-L-lysine concentration, hydrophobic interactions must have been involved to explain the binding of excess polypeptide. There seemed to be a penetration of poly-L-lysine in the bilayer that increased with the polypeptide concentration. Under these conditions, the chain-packing lattice gradually changed from hexagonal to either orthorhombic or monoclinic symmetry. We believe that this change of structure is associated with the interdigitation of the acyl chains.

Apollo 11 Drive-Tube Core Samples: An Initial Physical Analysis of Lunar Surface Sediment

Two drive-tube core samples were obtained at Tranquillity Base. Fines include much glass, are unweathered, medium gray, loose, nonstructured, very weakly coherent, and demonstrate both accumulation and mixing in a waterless vacuum environment. In contrast to chemical weathering characteristic on the earth, lunar alteration processes are primarily mechanical. We infer that environmental processes of the lunar surface may be expressed as follows: R (regolith) = f(cl, p, r, t, b, a, . . .), in which climate (cl) is constant and the time (t)-de-pendent processes of bombardment (b) and accumulation (a) assume significance unparalleled on the earth because of their effects on parent material (p) and relief (r).