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E London

Publications and source records attributed to E London.

At least 91 records · Page 5Linked to original sources
PubMed1982

Investigation of membrane structure using fluorescence quenching by spin-labels. A review of recent studies.

Fluorescence quenching is the loss of fluorescence intensity which is observed when a fluorescent molecule or group interacts with another molecule or group, called the quencher. By use of tryptophan residues of proteins, together with specific probe molecules, quenching can be applied to problems of biological and model membrane structure. Quenching interactions are short range (less than 50 A) so that structure on the scale of molecular dimensions can be examined. This review summarizes the recent applications of fluorescence quenching by spin (nitroxide)-labeled molecules to problems of membrane structure, including determination of the distance of membrane-bound molecules from the membrane surface, the strength of lipid-protein interactions and the strength of protein-protein interactions within membranes. The unique advantages and the limitations of this powerful method are examined.

Animals↗
PubMed1982

Denaturation and renaturation of bacteriorhodopsin in detergents and lipid-detergent mixtures.

The denatured and renatured states of bacteriorhodopsin have been studied in detergents and lipid/detergent mixtures by using ultraviolet and visible light absorption spectroscopy, fluorescence spectroscopy, and circular dichroism. Upon solubilization in sodium dodecyl sulfate, bacteriorhodopsin undergoes denaturation with partial loss of the secondary structure and loss of retinal binding ability. In contrast, delipidated bacteriorhodopsin retains its native structure in deoxycholate and undergoes denaturation only on photobleaching, which results in a partial loss of the secondary structure. Native secondary structure spontaneously reforms upon addition of phospholipid/cholate mixtures to bacterio-opsin denatured in sodium dodecyl sulfate. Upon subsequent addition of retinal, up to 95% of the native chromophore (lambdamax = 550-560 nm) is restored. Renaturation also restores the characteristics of light and dark adaptation and tight retinal binding (Kb greater than 10(7) M-1). Renaturation of delipidated bacteriorhodopsin denatured in sodium dodecyl sulfate also occurs without phospholipid upon the addition of retinal and Triton X-100 or octyl glucoside. The equilibrium between monomeric and oligomeric states of bacteriorhodopsin has been studied by circular dichroism and fluorescence quenching. Bacteriorhodopsin renatured with Triton X-100 or phospholipid/cholate is monomeric. However, removal of the detergents from renatured protein under specific conditions results in formation of an oligomer in which quaternary interactions are regenerated. The application of fluorescence quenching to the determination of oligomeric size in intrinsic membrane proteins is discussed.

Bacteriorhodopsins↗
PubMed1982

Two-dimensional echocardiographic analysis of segmental left ventricular wall motion before and after coronary artery bypass surgery.

Twenty patients with coronary artery disease were studied with two-dimensional echocardiography the day before saphenous vein bypass graft surgery. Serial studies were obtained 7.4 +/- 2.5 (+/- SD) and 43.4 +/- 13.1 days postoperatively to qualitatively assess the effect of bypass surgery on regional wall motion. Changes in segmental wall motion were assessed semiquantitatively by assigning a segmental wall motion score to each of nine echocardiographically defined segments. Preoperatively, 18% of the segments moved abnormally. The mean overall segmental wall motion score did not change significantly, as shown by comparing the postoperative studies with the preoperative study. However, there was a significant worsening in the septal motion (apical and basal) and a significant improvement in posterior wall motion (apical and basal) after bypass surgery. Anterior and lateral wall motion were not significantly changed. Nonseptal segments that were normal preoperatively usually remained normal; abnormal nonseptal segments usually improved or were unchanged by surgery. The motion of septal segments, however, generally worsened postoperatively whether they were normal or abnormal preoperatively. We conclude that segmental wall motion assessed by two-dimensional echocardiography may improve after revascularization surgery, but the interventricular septum shows impaired motion. This effect of coronary artery bypass on wall motion is better demonstrated relatively late after operation than early in the postoperative course, as has been done in some previous studies.

Aged↗
PubMed1981

Refolding of an integral membrane protein. Denaturation, renaturation, and reconstitution of intact bacteriorhodopsin and two proteolytic fragments.

The complete denaturation and subsequent renaturation and reconstitution of a polytopic integral membrane protein are demonstrated. Delipidated bacteriorhodopsin (Huang, K.-S., Bayley, H., and Khorana, H. G. (1980) Proc. Natl. Acad. Sci. U. S. A. 77, 323-327) is completely denatured when transferred into 88% formic acid or anhydrous trifluoroacetic acid as shown by NMR and circular dichroism spectroscopy. When ethanol is added to a solution of the denatured protein, helical structure is largely reformed. After neutralization of the acid with ammonia and dialysis against a solution of sodium dodecyl sulfate a substantial amount of this structure is retained. Complete renaturation, characterized by the formation of the chromophore, occurs when phospholipids, cholate, and retinal are added to the sodium dodecyl sulfate solution of the protein. After dialysis of the solution to remove the detergents, the bacteriorhodopsin assembles into vesicles that are fully active in light-driven proton translocation. We also show that two chymotryptic fragments of bacteriorhodopsin (residues 1-71 and 72-248), separated under denaturing conditions, can be made to reassociate and form active vesicles with phospholipids.

Apoproteins↗
PubMed1981

Fluorescence quenching in model membranes. 1. Characterization of quenching caused by a spin-labeled phospholipid.

A new method is described to evaluate contact between fluorophors and lipids in model membranes. This method utilizes a nitroxide spin-labeled phosphatidylcholine to quench th fluorescence from a variety of membrane-bound molecules by a static process. The distance dependence of the fluorescence quenching is analyzed in terms of simple models. The analysis shows that quenching of diphenylhexatriene, p-terphenyl, and molecules containing tryptophan arises only from spin-labeled phospholipid that is in contact with the fluorophor.

Dimyristoylphosphatidylcholine↗
PubMed1981

Fluorescence quenching in model membranes. 2. Determination of local lipid environment of the calcium adenosinetriphosphatase from sarcoplasmic reticulum.

Fluorescence quenching by spin-labeled phospholipid is used to determine the affinities of different phospholipids species to an intrinsic membrane protein, the Ca2+-ATPase of sacroplasmic reticulum. The phospholipids in contact with the Ca2+ ATPase are examined in a reconstituted system in which the enzyme is incorporated into a model membrane of defined phospholipid composition. The local phospholipid environment of the protein is considered to be governed at each phospholipid binding site by an equilibrium: lipid A + (lipid B - protein) in equilibrium or formed from lipid B + (lipid A - protein). Phospholipid binding constants to the Ca2+ ATPase can be obtained from an analysis of fluorescence quenching data. The binding constants for a number of phospholipid species are nearly identical when the phospholipids are in the liquid-crystal state. However, temperature of Ca2+-induced phase separation of phospholipid induces striking changes in the composition of the phospholipids in contact with the Ca2+ATPase, relative to the overall composition of the membranes. The implications of these results with respect to the control of local phospholipids environment by intrinsic membrane proteins and the nature of the phospholipids binding sites on the proteins are discussed. General applicability of this type of fluorescence quenching study to the problem of lipid-protein interactions in membranes is considered, and this method is compared to other techniques.

Animals↗
PubMed1981

Hospital crisis.

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Hospitals, Municipal↗
PubMed1979

Evaluation of the echocardiogram as an epidemiologic tool in an asymptomatic population.

An asymptomatic adult population of 196 men and women was studied with the echocardiogram to derive age- and sex-specific "normal" values for a number of clinically used echocardiograhic variables. The results are in general agreement with previously published normal values. Body position during the examination, age and sex influence the echocardiographic results; body surface area correction normalized most of these effects. The prevalence of occult abnormalities determined by the echocardiogram is 7%; the most common finding was mitral valve prolapse. Inter- and intraobserver variability was assessed. The interobserver differences found on analysis are statistically, but not clinically , significant. The echocardiogram appears to be a suitable tool to use in epidemiologic studies to detect selected cardiac abnormalities, but is limited for this purpose because some subjects in such a population cannot be adequately examined.

Adult↗
PubMed1979

Phosphorus NMR analysis of phospholipids in detergents.

Various detergents can be used to dissolve phospholipids, resulting in very narrow 31PNMR resonances. The resonances are well resolved, allowing identification and quantitative analysis of phospholipids in a mixture. The chemical shift depends strongly on pH, reflecting changes in the state of ionization of the phospholipid headgroup moieties. Samples of phospholipids dissolved in aqueous detergents are conveniently prepared and give narrower 31P resonances than do phospholipids dissolved in organic solvents.

Cholic Acids↗
PubMed1978

Pericardial effusions in patients with end-stage renal disease.

Echocardiography has greatly increased the accurate recognition of pericardial effusion. Echocardiograms were performed prospectively on the total group of 35 stable asymptomatic patients on chronic haemodialysis to determine the incidence of pericardial effusion. Effusions were shown in 11 per cent (4/35); only 6 per cent (2/35) were estimated as greater than 100 ml. For comparison, records were reviewed retrospectively from 41 haemodialysis patients referred during a 27-month period for echocardiographic assessment of suspected pericardial effusion. These 41 patients came from a total group of 108 patients treated with chronic dialysis over this interval. Of 41 examined, 21 (51%) or 21 of 108 (19%) of the population at risk had an effusion. Of 21 with echocardiographic effusions, 15 (71%), or 15 of 41 (37%) of those with clinically suspected effusion, had more than 100 ml fluid. Gross (greater than 100 ml) pericardial effusions are infrequent in stable, asymptomatic patients with end-stage renal disease. When clinical findings suggest pericardial disease, the echocardiographic demonstration of over 100 ml pericardial fluid is indicative of new effusion, rather than coincidental pre-existing effusion.

Echocardiography↗
PubMed1976

Mitral valve prolapse in one hundred presumably healthy young females.

Clinical, electrocardiographic, phonocardiographic, and echocardiographic examinations were performed in 100 presumably healthy young females. Treadmill testing and ambulatory electrocardiographic monitoring were performed in a selected group of these subjects. Phonocardiograms, recorded with the subjects supine at rest, after inhalation of amyl nitrite, and in the upright position, revealed a 17% incidence of nonejection clicks and/or late or mid- to late systolic murmurs (PHONO-MSCLSM). Echocardiographic studies were performed in the second, third, fourth, and fifth intercostal space with emphasis on the importance of transducer angulation on the chest. Studies obtained with the transducer perpendicular to the chest in the sagittal plane, or pointing cephalad at a time when both mitral leaflets and left atrium are recorded, are optimal to study the mitral valve systolic motion. With the transducer in this position, 21 subjects were found to have pansystolic or late systolic prolapse, as previously defined on the echocardiogram. The presence of these echocardiographic findings was statistically related to the presence of PHONO-MSCLSM. Other echocardiographic patterns were identified and their relation to PHONO-MSCLSM and transducer position is discussed. Ten subjects with both echocardiographic evidence of mitral valve prolapse and PHONO-MSCLSM were identified (group EP), while 18 other subjects had either echocardiographic or phonocardiographic findings suggestive of mitral valve abnormality (group EorP). Seventy-two subjects had no abnormality (group noEP). The incidence of various clinical, electrocardiographic, and echocardiographic findings in these three groups was determined. Some findings said to be common in patients with proven mitral valve prolapse were seen more frequently in group EP subjects. Echocardiographic and phonocardiographic findings suggesting mitral valve abnormalities were found more commonly than expected in a population of presumably healthy young females.

Adolescent↗
PubMed1976

Effect of transducer placement on echocardiographic mitral valve systolic motion.

The influence of transducer position and angulation upon the mitral systolic echo was studied in 100 presumably healthy females. Echocardiographic studies were performed from the second, third, fourth and fifth intercostal spaces (ICS). The role of the sound beam's path relative to cardiac motion was assessed by analyzing the recorded mitral valve pattern as a function of transducer orientation, independent of the absolute ICS used. With the transducer directed caudally when both mitral leaflets and left atrium were recorded, holosystolic or midsystolic posterior motion of the mitral valve leaflet echo was seen in 59% of the subjects. These patterns, recorded this way, were not related to phonocardiographic signs suggesting mitral valve prolapse. Best correlation with phonocardiographic findings was obtained when the echocardiographic examination was performed with the transducer either perpendicular to the chest in the sagittal plane, or pointing slightly cephalad ('perpendicular' position). With the transducer in 'perpendicular' position, both holosystolic and midsystolic posterior motion of the mitral systolic echo, deviating more than 2 mm from a line joining the C and D points, were highly related statistically to phonocardiographic findings suggesting mitral valve prolapse. This study demonstrates that transducer position and angulation on the chest wall are important determinants of echocardiographic appearance of mitral valve during systole. Only the 'perpendicular' transducer position should be used when analyzing echocardiograms for the presence of mitral valve prolapse.

Echocardiography↗