Pressure Effects on Liposomes, Biological Membranes and Membrane-Bound Proteins

Abstract

124 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1982.The phosphatidylcholine vesicles were examined by steady state polarization fluorometry under pressure in the range of 1 bar to 2 Kbar. Isothermal pressure-induced phase transitions were observed in dipalmitoylphosphaditylcholine and dimyristoylphosphatidylcholine vesicles incorporated with 1,6-diphenyl-1,3,5-hextriene (DPH). The temperature-to-pressure equivalence, dT/dP, estimated from the transition point, P(, 1/2), is between 21-30(DEGREES)Kbar('-1). Even though there is no phase transition, I am still able to estimate a dT/dP of 21(DEGREES)Kbar('-1) for dioleoylphosphatidylcholine multilamellar vesicles.The effects of pressure upon the fluidity and order of the synaptic membrane fractions of goldfish brain have been studied by using steady state and differential polarized phase fluorometry. Membrane order became progressively greater as pressure was increased up to approximately 2 Kbar. An increase in pressure of 1 Kbar had an effect on membrane order that was equivalent to a 13-19(DEGREES)C reduction in temperature. At 5.6(DEGREES)C, pressurization caused a large increase in the rotational rate of molecules. It is suggested that this is due to the segregation of probe molecules in highly ordered membranes, which either leads to excitation transfer between DPH molecules or to changes in the rotational motion of DPH from "sticking" to "slipping".The enzyme activities of the (Na('+)+K('+))-ATPase isolated from dog kidney were measured under pressure. The apparent K-pNPPase activity decreases with pressure, giving a dT/dP value of 22(DEGREES)Kbar('-1). The Na-K ATPase activity also decreases with pressure with a dT/dP of 16-21(DEGREES)Kbar('-1). The enzyme activities were then correlated with membrane fluidity by measurements of the change of steady state fluorescence polarization of DPH and perylene in ATPase membranes under pressure which itself showed dT/dP = 18-21(DEGREES)Kbar('-1). A direct relation between membrane fluidity and enzyme activity has been clearly demonstrated with temperature and pressure as thermodynamic variables in the (Na('+)+K('+))-ATPase.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD