Biomedical subjects

E C Melo

Publications and source records attributed to E C Melo.

4 recordsLinked to original sources

PubMed1992

Effects of domain connection and disconnection on the yields of in-plane bimolecular reactions in membranes.

It has recently been shown (Vaz, W.L.C., E.C.C. Melo, and T.E. Thompson. 1989. Biophys. J. 56:869-875; 1990. Biophys. J. 58:273-275) that in lipid bilayer membranes in which ordered and disordered phases coexist, the ordered phase can form a two-dimensional reticular structure that subdivides the coexisting disordered phase into a disconnected domain structure. Here we consider theoretically the yields of bimolecular reactions between membrane-localized reactants, when both the reactants and products are confined to the disordered phase. It is shown that compartmentalization of reactants in disconnected domains can lead to significant reductions in reaction yields. The reduction in yield was calculated for classical bimolecular processes and for enzyme-catalyzed reactions. These ideas can be used to explain certain experimental observations.

Biophysical Phenomena↗

PubMed1991

Fluid-phase connectivity and translational diffusion in a eutectic, two-component, two-phase phosphatidylcholine bilayer.

In recent work [Vaz, W.L.C., Melo, E.C.C., & Thompson, T.E. (1989) Biophys. J. 56, 869-876] we have shown that translational diffusion studies using fluorescence recovery after photobleaching (FRAP) provide information concerning domain structures and fluid-phase connectivity in lipid bilayers in which solid and fluid phases coexist. In the present paper, translational diffusion of the fluid-phase-soluble, solid-phase-insoluble fluorescent lipid derivative N-(7-nitrobenzoxa-2,3-diazol-4-yl) dilauroyl-phosphatidylethanolamine and the fluid-phase connectivity are examined in lipid bilayers prepared from binary mixtures of 1-docosanoyl-2-dodecanoylphosphatidylcholine (C22:0C12:0PC) and 1,2-diheptadecanoylphosphatidylcholine (di-C17:0PC) by using FRAP. The phosphatidylcholine mixture used provides a eutectic system with a eutectic point at a composition of about 0.4 mole fraction of di-C17:0PC and a temperature of about 37 degrees C [Sisk, R.B., Wang, Z.Q., Lin, H.N., & Huang, C.H. (1990) Biophys. J. 58, 777-783]. Two regions in temperature and composition, respectively below and above 0.4 mole fraction of di-C17:0PC, where fluid and solid phases coexist in the same lipid bilayer, are available for examination of fluid-phase connectivity. In mixtures containing less than 0.4 mole fraction of di-C17:0PC the fluid phase coexists with a mixed interdigitated Lc gel phase composed mostly of C22:0C12:0PC, whereas in mixtures containing greater than 0.4 mole fraction of di-C17:0PC the fluid phase coexists with a P beta' gel phase mostly composed of di-C17:0PC. When the solid phase is a P beta' gel phase, the temperature of fluid-phase connectivity for the mixtures lies close to the fluidus, which means that a small (approximately 20%) mass fraction of solid phase can divide the large bulk of the bilayer that is fluid into nonconnected domains.(ABSTRACT TRUNCATED AT 250 WORDS)

Diffusion↗

PubMed1990

Fluid phase connectivity in an isomorphous, two-component, two-phase phosphatidylcholine bilayer.

Two-dimensional fluid phase connectivity is examined in mixed bilayers of dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine as a function of composition and temperature at constant pressure using fluorescence recovery after photobleaching (FRAP). These isomorphous phospholipid mixtures exhibit nearly ideal mixing behavior. Dilauroyl phosphatidylethanolamine covalently linked through its amino function to NBD is used as the fluorescent probe in this study. These studies show the line of connectivity to be coincident with the line connecting the midpoints of all tie lines in the two-phase region of the phase diagram.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed1989

Translational diffusion and fluid domain connectivity in a two-component, two-phase phospholipid bilayer.

The two-dimensional connectivity is examined for mixed bilayers of dimyristoyl phosphatidylcholine (DMPC) and distearoyl phosphatidylcholine (DSPC) as a function of composition and temperature at constant pressure using the fluorescence recovery after photobleaching (FRAP) method. These phospholipid mixtures exhibit peritectic behavior with a large region in which both gel and liquid crystalline phases coexist. Dilauroyl phosphatidylethanolamine covalently linked through the amino function in its head group to the fluorescent nitrobenzodiazolyl group (NBD-DLPE) was used as the fluorescent probe in this study, because it was found to partition almost exclusively in the liquid crystalline phase. The results of these studies show the line of connectivity to be close to the liquidus line on the phase diagram over a rather broad range of concentrations. In this range, a gel phase comprising approximately 20% of the system disconnects a liquid crystalline phase comprising 80% of the system. The implications of this result are discussed for domain shape and the organization of biological membrane components.

4-Chloro-7-nitrobenzofurazan↗