Biomaterial Database

Temperature dependence of light-induced proton movement in reconstituted purple membrane. 1984

S I Tu, and H Hutchinson

Bacteriorhodopsin (BR) was incorporated into phosphatidylcholine (PC) vesicles containing different amounts of other lipids. Under the conditions of nullified membrane potential, light-induced proton movement seemed to follow a kinetic scheme which assumed the existence of a proton-pumping inhibition process characterized by a rate constant, kI. The temperature dependence of both kI and the membrane proton leak rate constant (kD) obeyed a simple Arrhenius equation. The presence of cholesterol in the membrane significantly increased the activation energy (Ea) of both the inhibition and leak process. However, further addition of phosphatidic acid (PA) suppressed the increase of Ea associated with kI. The initial proton pumping rate (R0) of vesicles reconstituted with PC showed a bell-shaped temperature dependence with a maximum at approximately 20 degrees C. The addition of cholesterol abolished this dependence. These results suggest that the molecular origin of the inhibition process characterized by kI is different from that of R0 or kD. The temperature dependence of the steady-state fluorescence polarization of dansylated bacteriorhodopsin in vesicles was also investigated. The polarization of the labels in the vesicles without cholesterol showed a bell-shaped temperature dependence with a maximum at approximately 20 degrees C. However, in the presence of cholesterol, the polarization increased linearly as temperature decreased. A comparison of these results with the observed proton movement in similarly reconstituted systems with unmodified protein indicates that membranes with a low fluidity and negatively charged surfaces enhance proton pumping efficiency of bacteriorhodopsin.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008027	Light	That portion of the electromagnetic spectrum in the visible, ultraviolet, and infrared range.	Light, Visible,Photoradiation,Radiation, Visible,Visible Radiation,Photoradiations,Radiations, Visible,Visible Light,Visible Radiations
D010743	Phospholipids	Lipids containing one or more phosphate groups, particularly those derived from either glycerol (phosphoglycerides see GLYCEROPHOSPHOLIPIDS) or sphingosine (SPHINGOLIPIDS). They are polar lipids that are of great importance for the structure and function of cell membranes and are the most abundant of membrane lipids, although not stored in large amounts in the system.	Phosphatides,Phospholipid
D011522	Protons	Stable elementary particles having the smallest known positive charge, found in the nuclei of all elements. The proton mass is less than that of a neutron. A proton is the nucleus of the light hydrogen atom, i.e., the hydrogen ion.	Hydrogen Ions,Hydrogen Ion,Ion, Hydrogen,Ions, Hydrogen,Proton
D002338	Carotenoids	The general name for a group of fat-soluble pigments found in green, yellow, and leafy vegetables, and yellow fruits. They are aliphatic hydrocarbons containing 4 terpene subunits.	Carotenes,Carotenoid,Tetraterpene Derivatives,Tetraterpenes,Carotene,Derivatives, Tetraterpene
D005454	Fluorescence Polarization	Measurement of the polarization of fluorescent light from solutions or microscopic specimens. It is used to provide information concerning molecular size, shape, and conformation, molecular anisotropy, electronic energy transfer, molecular interaction, including dye and coenzyme binding, and the antigen-antibody reaction.	Anisotropy, Fluorescence,Fluorescence Anisotropy,Polarization, Fluorescence,Anisotropies, Fluorescence,Fluorescence Anisotropies,Fluorescence Polarizations,Polarizations, Fluorescence
D006217	Halobacterium	A genus of HALOBACTERIACEAE whose growth requires a high concentration of salt. Binary fission is by constriction.
D001436	Bacteriorhodopsins	Rhodopsins found in the PURPLE MEMBRANE of halophilic archaea such as HALOBACTERIUM HALOBIUM. Bacteriorhodopsins function as an energy transducers, converting light energy into electrochemical energy via PROTON PUMPS.	Bacteriorhodopsin
D001693	Biological Transport, Active	The movement of materials across cell membranes and epithelial layers against an electrochemical gradient, requiring the expenditure of metabolic energy.	Active Transport,Uphill Transport,Active Biological Transport,Biologic Transport, Active,Transport, Active Biological,Active Biologic Transport,Transport, Active,Transport, Active Biologic,Transport, Uphill
D013696	Temperature	The property of objects that determines the direction of heat flow when they are placed in direct thermal contact. The temperature is the energy of microscopic motions (vibrational and translational) of the particles of atoms.	Temperatures