Electron spin-echo studies of spin-labelled lipid membranes and free fatty acids interacting with human serum albumin.
Human serum albumin (HSA) is an abundant plasma protein that transports fatty acids and also binds a wide variety of hydrophobic pharmacores. Echo-detected (ED) EPR spectra and D(2)O-electron spin echo envelope modulation (ESEEM) Fourier-transform spectra of spin-labelled free fatty acids and phospholipids were used jointly to investigate the binding of stearic acid to HSA and the adsorption of the protein on dipalmitoyl phosphatidylcholine (DPPC) membranes. In membranes, torsional librations are detected in the ED-spectra, the intensity of which depends on chain position at low temperature. Water penetration into the membrane is seen in the D(2)O-ESEEM spectra, the intensity of which decreases greatly at the middle of the membrane. Both the chain librational motion and the water penetration are only little affected by adsorption of serum albumin at the DPPC membrane surface. In contrast, both the librational motion and the accessibility of the chains to water are very different in the hydrophobic fatty acid binding sites of HSA from those in membranes. Indeed, the librational motion of bound fatty acids is suppressed at low temperature, and is similar for the different chain positions, at all temperatures. Correspondingly, all segments of the bound chains are accessible to water, to rather similar extents.
De Simone
Francesco
F
Dipartimento di Fisica, Laboratorio di Biofisica Molecolare and UdR CNISM, Università della Calabria, I-87036 Arcavacata di Rende, CS, Italy.
Guzzi
Rita
R
Sportelli
Luigi
L
Marsh
Derek
D
Bartucci
Rosa
R
D015060:1,2-Dipalmitoylphosphatidylcholine / Q000737:chemistry; D000327:Adsorption; D004578:Electron Spin Resonance Spectroscopy; D005230:Fatty Acids, Nonesterified / Q000737:chemistry; D006801:Humans; D008566:Membranes / Q000737:chemistry*; D008958:Models, Molecular; D010743:Phospholipids / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry*; D013229:Stearic Acids / Q000737:chemistry*; D013696:Temperature
D005230:Fatty Acids, Nonesterified; D010743:Phospholipids; D012709:Serum Albumin; D013229:Stearic Acids; D015060:1,2-Dipalmitoylphosphatidylcholine