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M Caffrey

Publications and source records attributed to M Caffrey.

At least 91 records · Page 5Linked to original sources
PubMed1988

X-ray standing waves: a molecular yardstick for biological membranes.

Structural information on an atomic scale has been obtained for a Langmuir-Blodgett (LB) trilayer system by means of long-period x-ray standing waves. The LB trilayer of zinc and cadmium arachidate was deposited on a layered synthetic microstructure (LSM) consisting of 200 tungsten/silicon layer pairs with a 25 A period. A 30 A thermally induced inward collapse of the zinc atom layer that was initially located in the LB trilayer at 53 A above the LSM surface has been observed. The mean position and width of the zinc atom layer was determined with a precision of +/- 0.3 A.

Membranes↗
PubMed1988

Lipid-sugar interactions : relevance to anhydrous biology.

The ability of seeds and other anhydrous plant forms to survive the withdrawal of water must involve a mechanism for protecting the integrity of cellular membranes. Evidence from animal systems implicates sugars as protective components, and we have tested the changes in mesomorphic phase state of phospholipid model membranes upon hydration and dehydration in the presence of sucrose and/or sucrose plus raffinose. X-ray diffraction studies of dry dimyristoylphosphatidylcholine (DMPC) indicate that the presence of sucrose lowers the chain order/disorder transition temperature to that of hydrated lipid; likewise, the lamellar repeat spacings showed the dry DMPC/sucrose mixture to be similar to that of the hydrated lipid. These results support the proposed potential of sugars to substitute for water in biomembranes. If sucrose is to serve as a protectant during desiccation of seeds, its tendency to crystallize would lessen its effectiveness. Raffinose is known to serve as an inhibitor of sucrose crystallization, and is abundant in seeds. The addition of raffinose to make DMPC/sucrose/raffinose mixtures (1/1/0.3 mass ratio) prevented sucrose crystallization, suggesting this as a possible in vivo role for raffinose.

Journal Article↗
PubMed1987

Kinetics and mechanism of transitions involving the lamellar, cubic, inverted hexagonal, and fluid isotropic phases of hydrated monoacylglycerides monitored by time-resolved X-ray diffraction.

A study of the dynamics and mechanism of the various thermotropic phase transitions undergone by the hydrated monoacylglycerides monoolein and monoelaidin, in the temperature range of 20-120 degrees C and from 0 to 5 M NaCl, has been undertaken. Measurements were made by using time-resolved X-ray diffraction at the Cornell High-Energy Synchrotron Source. The lamellar chain order/disorder, lamellar/cubic (body centered, space group No. 8), cubic (body centered, No. 8)/cubic (primitive, No. 4), cubic (body centered, No. 12)/cubic (primitive, No. 4), cubic (primitive, No. 4)/fluid isotropic, cubic (body centered, No. 12)/inverted hexagonal, cubic (primitive, No. 4)/inverted hexagonal, and hexagonal/fluid isotropic transitions were examined under active heating and passive cooling by using a jump in temperature to effect phase transformation. All of the transitions with the exception of the cubic (body centered, No. 8)/cubic (primitive, No. 4) and the cubic (body centered, No. 12)/cubic (primitive, No. 4) cooling transitions were found (1) to be repeatable, (2) to be reversible, and (3) to have an upper bound on the transit time (time required to complete the transition) of less than or equal to 3 s. The shortest transit times recorded for the various phase changes in the heating direction were less than or equal to 1.9 (lamellar chain melting), less than or equal to 1.7 [lamellar liquid crystal/cubic (body (body centered, No. 8)], less than or equal to 0.5 [cubic (body centered, No. 8)/cubic (primitive, No. 4)], less than or equal to 0.9 [cubic (primitive, No. 4)/hexagonal], less than or equal to 1.3 [cubic (body centered, No. 12)/cubic (primitive, No. 4) and cubic (body centered, No. 12)/hexagonal], and less than or equal to 0.6 s (hexagonal/fluid isotropic). For the exceptions noted above, the transitions were slow with transit times ranging from 0.5 to 30 min and displayed pronounced hysteresis and/or undercooling. Regardless of the direction of the transitions, all but one appear to be two state to within the sensitivity limits of the time-resolved method. In the case of the lamellar liquid crystal/cubic (body centered, No. 8) transition a stable intermediate of unknown identity was apparent. In addition to the time-resolved measurements, data were obtained on the stability of the various phases in the temperature range of 20-120 degrees C and from 0 to 5 M NaCl. In the case of fully hydrated monoolein, high salt strongly favors the hexagonal over the cubic (body centered, No. 8) phase and slightly elevates the hexagonal/fluid isotropic transition temperature.(ABSTRACT TRUNCATED AT 400 WORDS)

Glycerides↗
PubMed1987

A crystalline lipid phase in a dry biological system: evidence from X-ray diffraction analysis of Typha latifolia pollen.

The temperature limits for germination in Typha latifolia pollen lie within the range 4-40 degrees C. These limits correlate at the low-temperature end with the 'crystallization' of endogenous triacylglycerols and on the high-temperature end with the 'melting' of a gel-like lipid component in intact pollen. X-ray diffraction analysis was used to structurally characterize and to trace the latter gel-like lipid from the intact pollen through a range of pollen lipid fractions. We tentatively identify this component as a fatty acyl sterol ester and present evidence that it resides in the exine of the pollen grain. Its thermotropic behavior is insensitive to pollen hydration. The possibility of interpreting a crystalline lipid phase as being membrane-derived when in fact it originates from contaminating non-membranous neutral lipid is discussed. The total lipid content of T. latifolia pollen is 123 mg/g dry weight, of which 37% is polar lipid. The neutral lipid consists primarily of triacylglycerols and of the aforementioned sterol ester, which represents 0.34% (w/w) of pollen dry weight. The polar lipid fraction has phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid as major components with lesser amounts of phosphatidylglycerol and phosphatidylinositol. Palmitic (16:0) and linoleic (18:2) acids, in a 1:2 molar ratio, constitute the major fatty acids of both polar and neutral lipid fractions with lesser amounts of linolenic (18:3), oleic (18:1) and stearic (18:0) acid in evidence.

Chromatography, Thin Layer↗
PubMed1987

Effect of chlorophyll a on the phase behavior of hydrated monogalactosyldiacylglycerols.

We have studied the effect of chlorophyll a (chl a) on the X-ray diffraction patterns and the appearance of freeze-fracture electron micrographs of aqueous dispersions of monogalactosyldiacylglycerols (MGDG), the most abundant lipid in the thylakoid membrane. In MGDG systems containing 0-18 mol% of chl a, the diffraction patterns indicate the presence of a well-ordered reverse hexagonal phase. When 30 mol% of chl a was incorporated into the MGDG, the low-angle X-ray diffraction lines of the hexagonal lattice were slightly broadened and were accompanied by additional weak lines. With higher mol percents of chl a, the low-angle lines could no longer be indexed on a hexagonal or lamellar lattice. The freeze-fracture electron micrographs of similar samples showed that the patterns characteristic of the reverse hexagonal phase of an aqueous dispersion of pure MGDG were replaced by large liposomes, the fracture pattern of which is circular. We conclude that chl a in excess of 20 mol% destabilized the orderly reverse hexagonal phase of aqueous MGDG dispersions and disturbed the long-range order of the lipid array. These results are summarized in a temperature-composition isobaric phase diagram over a temperature range of -60 degrees C to 60 degrees C.

Chlorophyll↗
PubMed1987

The combined and separate effects of low temperature and freezing on membrane lipid mesomorphic phase behavior: relevance to cryobiology.

Time-resolved X-ray diffraction is used to demonstrate that for certain lipids low temperature alone may not be sufficient to bring about changes in mesomorphic phase state. However, when combined with slow freezing of the aqueous substrate, the fluid bilayer phase is destabilized as a result of dehydration, and thus more prone to undergoing deleterious thermotropic phase transformations. The cryobiological relevance of these results is discussed.

Freezing↗
PubMed1987

Uranyl acetate induces gel phase formation in model lipid and biological membranes.

The effect of uranyl acetate on the mesomorphic phase state of lipids in model membranes as well as in isolated biological membranes has been examined. As little as 0.8 mM (0.03% [wt/vol]) uranyl acetate induces a liquid crystal-to-gel phase transformation in egg phosphatidic acid, bovine brain phosphatidylserine, and in lysed chromaffin granule membranes. These results along with others in the literature indicate that the uranyl acetate used in samples for electron microscopy could alter membrane morphology.

Adrenal Medulla↗
PubMed1987

A temperature gradient method for lipid phase diagram construction using time-resolved x-ray diffraction.

A method that enables temperature-composition phase diagram construction at unprecedented rates is described and evaluated. The method involves establishing a known temperature gradient along the length of a metal rod. Samples of different compositions contained in long, thin-walled capillaries are positioned lengthwise on the rod and "equilibrated" such that the temperature gradient is communicated into the sample. The sample is then moved through a focused, monochromatic synchroton-derived x-ray beam and the image-intensified diffraction pattern from the sample is recorded on videotape continuously in live-time as a function of position and, thus, temperature. The temperature at which the diffraction pattern changes corresponds to a phase boundary, and the phase(s) existing (coexisting) on either side of the boundary can be identified on the basis of the diffraction pattern. Repeating the measurement on samples covering the entire composition range completes the phase diagram. These additional samples can be conveniently placed at different locations around the perimeter of the cylindrical rod and rotated into position for diffraction measurement. Temperature-composition phase diagrams for the fully hydrated binary mixtures, dimyristoylphosphatidylcholine (DMPC)/dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylethanolamine (DPPE)/DPPC, have been constructed using the new temperature gradient method. They agree well with and extend the results obtained by other techniques. In the DPPE/DPPC system structural parameters as a function of temperature in the various phases including the subgel phase are reported. The potential limitations of this steady-state method are discussed.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1986

Redox pathways in electron-transfer proteins: correlations between reactivities, solvent exposure, and unpaired-spin-density distributions.

The relative reactivities toward reduction by free flavin semiquinones of cytochromes (c-type cytochromes, cytochrome b5, c'-type cytochromes) iron-sulfur proteins (high-redox-potential ferredoxins, rubredoxins, low-redox-potential ferredoxins), and blue copper proteins (plastocyanin, azurins) are shown to correlate with calculations of the solvent exposure of the various prosthetic groups. In the case of the c-type cytochromes, one of the major centers of exposure is the sulfur atom of the thioether bridge that covalently links heme ring C to the protein. Charge-iterative extended Hückel calculations on a heme c model indicate that both porphyrin pi and Fe(III)d pi orbitals can delocalize onto the bridging sulfur atom. Unpaired spin densities are comparable to those obtained for individual aromatic porphyrin ring carbon atoms. Thus, the exposed sulfur of ring C may act to facilitate electron transfer.

Animals↗
PubMed1985

Kinetics and mechanism of the lamellar gel/lamellar liquid-crystal and lamellar/inverted hexagonal phase transition in phosphatidylethanolamine: a real-time X-ray diffraction study using synchrotron radiation.

A study of the kinetics and mechanism of the thermotropic lamellar gel/lamellar liquid-crystalline and lamellar/inverted hexagonal phase transition in dihexadecylphosphatidylethanolamine (DHPE) at various hydration levels has been carried out. Measurements were made by using a real-time X-ray diffraction method at the Cornell High Energy Synchrotron Source. This represents an extension of an earlier study concerning the lamellar gel/lamellar liquid-crystalline phase transition in dipalmitoylphosphatidylcholine [Caffrey, M., & Bilderback, D. H. (1984) Biophys. J. 45, 627-631]. With DHPE, the chain-melting and the nonbilayer transitions were examined under active heating and passive cooling conditions by using a temperature jump to effect phase transformation. Measurements were made at hydration levels ranging from 0% to 60% (w/w) water, and in all cases, the transitions were found to be repeatable, be reversible, and have an upper bound on the transit times (time required to complete the transition) of less than or equal to 3 s. The shortest transit time recorded for the chain-melting and lamellar/hexagonal transitions was less than 1 s. At 8% (w/w) water, the transit times were still on the order of seconds even though the transition does not involve the intermediate L alpha phase. Note, the measured transit times are gross values incorporating the intrinsic transit time in addition to the time required to heat or cool the sample through the transition temperature range and to supply or remove the latent heat of the transition. Regardless of the direction of the transition, both appear to be two state to within the sensitivity limits of the real-time method. From simultaneous wide- and low-angle measurements at the lamellar chain-melting transition, loss of long-range order in the lamellar gel phase appears to precede the chain-melting process. On the basis of the real-time X-ray diffraction measurements, a mechanism is proposed for the lamellar/hexagonal phase transition. The mechanism does not involve large or energetically expensive molecular rearrangements, leads directly to a hexagonal lattice coplanar with the lamellar phase, incorporates facile reversibility, repeatability, and cooperativity, accounts for an observed, apparent memory in the hexagonal phase of the original lamellar phase orientation, and is consistent with the experimental observation of a predominantly two-state transition. In conjunction with the kinetic measurements, the DHPE/water phase diagram was constructed. At and above 12% (w/w) water, the thermotropic transition sequence is L beta'/L alpha/HII.(ABSTRACT TRUNCATED AT 400 WORDS)

Gels↗
PubMed1984

Influence of metal ions on the phase properties of phosphatidic acid in combination with natural and synthetic phosphatidylcholines: an X-ray diffraction study using synchrotron radiation.

Synchrotron radiation was used as an X-ray source of extreme brilliance to investigate by X-ray diffraction the phase behavior of fully hydrated unoriented samples of egg phosphatidic acid (egg PA) in combination with egg phosphatidylcholine (egg PC), dimyristoylphosphatidylcholine (DMPC), or dipalmitoylphosphatidylcholine (DPPC). The diffraction method was sensitive to greater than or equal to 2 mol % gel and greater than or equal to 30 mol % liquid-crystal phase lipid. Accordingly, the liquidus boundary was determined more exactly than the solidus boundary in these phase diagrams. A more precise location of the solidus line was obtained by monitoring the electron paramagnetic resonance signal from TEMPO partitioned between fluid lipid and aqueous phases. Phase diagrams for (i) egg PA/egg PC, (ii) egg PA/DMPC, and (iii) egg PA/DPPC with and without Cd2+ were determined in the temperature range 0-55 degrees C. In system i, the addition of Cd2+ raises the midpoint of the egg PA transition temperature range from 14 to 26 degrees C and results in a wide region of gel-liquid-crystal phase coexistence. With as little as 5 mol % egg PA in egg PC, Cd2+ induces phase separation up to about 25 degrees C. The phase behavior of egg PA/spin-labeled PC in the presence of Cd2+ was very similar to that of egg PA/egg PC in the 10-35 degrees C temperature range. In systems ii and iii Cd2+ extends the temperature range over which the gel and liquid-crystal phases coexist.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Kinetics of the main phase transition of hydrated lecithin monitored by real-time X-ray diffraction.

A method is described for observing and recording in real-time x-ray diffraction from an unoriented hydrated membrane lipid, dipalmitoylphosphatidylcholine (DPPC), through its thermotropic gel/liquid crystal phase transition. Synchrotron radiation from the Cornell High Energy Synchrotron Source (Ithaca, New York) was used as an x-ray source of extremely high brilliance and the dynamic display of the diffraction image was effected using a three-stage image intensifier tube coupled to an external fluorescent screen. The image on the output phosphor was sufficiently intense to be recorded cinematographically and to be displayed on a television monitor using a vidicon camera at 30 frames X s1. These measurements set an upper limit of 2 s on the DPPC gel----liquid crystal phase transition and indicate that the transition is a two-state process. The real-time method couples the power of x-ray diffraction as a structural probe with the ability to follow kinetics of structural changes. The method does not require an exogenous probe, is relatively nonperturbing, and can be used with membranes in a variety of physical states and with unstable samples. The method has the additional advantage over its static measurement counterpart in that it is more likely to detect transiently stable intermediates if present.

Chemical Phenomena↗
PubMed1981

Fluorescence quenching in model membranes. 3. Relationship between calcium adenosinetriphosphatase enzyme activity and the affinity of the protein for phosphatidylcholines with different acyl chain characteristics.

The dependence of function and lipid binding affinity of an integral transport protein on the fatty acyl chain characteristics of a membrane-forming phospholipid have been determined. When a newly developed fluorescence quenching technique [London, E., & Feigenson, G. W. (1981) Biochemistry (first paper of three in this issue); London, E., & Feigenson, G. W. (1981) Biochemistry (preceding paper in this issue)] is used for examining lipid-protein interactions in membranes, the Ca2+ ATPase from rabbit sarcoplasmic reticulum is found to bind with equal affinity a large variety of phosphatidylcholines used to reconstitute the protein into enzymatically active vesicles, regardless of fatty acyl chain length or details of unsaturation. In parallel with the lipid binding studies, we have measured the sensitivity of the catalytic activity of the Ca2+ ATPase to the fatty acyl chain characteristics of the phosphatidylcholine membranes in which the enzyme was reconstituted. The enzyme appears to be sensitive only to the effective fatty acyl chain length, which determines the thickness of the bilayer in which the protein is inserted and displays little sensitivity to such details of unsaturation as degree, position, and isomeric type. Both ATP hydrolyzing and Ca2+ transporting activities of the enzyme were similarly affected by bilayer thickness, and maximum activity was observed in membranes of intermediate thickness. These observations are reconciled in a number of possible models for the manner in which this integral protein interacts with membranes of varying thickness. A freeze-thaw method was used to reconstitute the Ca2+ ATPase, and the vesicles so obtained have been characterized by gel permeation chromatography, density gradient centrifugation, and electron microscopy, (thin section). Convenient methods are described for (a) rapidly separating reconstituted Ca2+ ATPase from unincorporated protein simultaneously in a large number of small samples, giving good recovery of fractionated vesicles without significant dilution, and (b) measuring leakiness to Ca2+ of reconstituted vesicles. Additionally, the gel and liquid-crystal phase transition temperature and bilayer thickness have been determined respectively by differential thermal analysis and low-angle X-ray diffraction for some of the synthetic phosphatidylcholines, which range in chain length from 12 to 24 carbon atoms.

Animals↗
PubMed1977

Kinetics of a micelle specific palmitoyltransferase isoenzyme of rabbit mammary gland.

Palmityl-CoA: monopalmityl-sn-glycerol 3-phosphate palmitoyltransferase [EC 2.3.1. -] in rabbit mammary gland microsomes is composed of two isoenzymic species. The alpha form (LPAT-alpha) is active with monomeric substrates and inhibited by micelles while the beta form (LPAT-beta) is active only with micelles. By combining the effects of time, temperature, and Tween 80 which selectively inhibited LPAT-alpha, the substrate saturation curve for the LPAT-beta isoenzyme has been successfully determined. Both theoretical and experimental curves are in good agreement.

Acyltransferases↗
PubMed1977

Growth and acyltransferase activity of rabbit mammary gland during pregnancy and lactation.

A bimodal change in yield and microsomal protein content of rabbit mammary gland was observed with the progress of pregnancy and lactation. The initial stimulus took place on day 22 of pregnancy and the second during early lactation. Palmitoyl-CoA:monopalmitoyl-sn-glycerol 3-phosphate palmitoyltransferase activity was monitored concurrently. This enzyme in rabbit mammary microsomes is composed of two isoenzymic species that differ with respect to the physical nature of the substrates with which each interacts. The activities of the two isoenzymes were recorded at progressive stages of pregnancy, lactation, and involution to determine if a regulatory role could be assigned to either or both species. Although the patterns were indefinite, total transacylase activity did increase over this period, i.e., the specific activity of LPAT-alpha was 12 and 24 nmoles/mg protein per min in pregnancy and lactation, respectively, while that of LPAT-beta rose from zero to 90 nmoles/mg protein per min over the same period. The time of harvesting in relation to the interval between nursing periods is discussed in the light of these results.

Acyltransferases↗