Conformational changes in bacteriorhodopsin accompanying ionophore activity
Planar membrane and liposome studies with bacteriorhodopsin in purple membrane fragments are reported. Results show that (1) the activity of bacteriorhodopsin in the purple membrane is increased, as judged by greater photopotentials across planar membranes or proton translocation in liposomes, by cations, particularly bivalent cations as Ca/sup 2 +/, and by applied electric fields. The effect of bivalent ions appears to be twofold, a direct effect on bacteriorhodopsin oriented in different directions and promoting interaction of liposomes at the planar membrane interface. Applied electrical fields appear to affect orientation of purple membranes at the planar membrane interface. (2) Polymer stabilized black lipid membranes will prove quite useful for extending this test system for the study of ionophore activity of biological catalysts. (3) Bacteriorhodopsin in the purple membrane patch exhibits considerable thermal stability and this intrinsic stability is enhanced by treatment with bifunctional cross-linking reagents. (4) After chemical modification of bacteriorhodopsin in the light- or dark-adapted state, differences in proton pump activity are found in bacteriorhodopsin liposomes; these differences are consistent with differences in the number of remaining free lysine and tryptophan residues. These results indicate that two conformational states of the protein of bacteriorhodopsin are involved in its functioning as an ionophore. (5) Studies with bifunctional cross-linking reagents having a defined chain length indicate that the proton is transferred through a channel and/or pore present in the interior of the bacteriorhodopsin molecule rather than by a translocation mechanism.
- Research Organization:
- Univ. of California, Berkeley
- OSTI ID:
- 5206836
- Journal Information:
- Fed. Proc.; (United States), Vol. 36:6
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
MEMBRANES
BIOCHEMICAL REACTION KINETICS
AMINO ACIDS
BACTERIA
CALCIUM IONS
CATIONS
ELECTRIC FIELDS
ELECTRIC POTENTIAL
ENERGY TRANSFER
HYDROGEN IONS
LYSINE
METABOLISM
PROTEINS
PROTONS
TRANSLOCATION
TRYPTOPHAN
VALENCE
ATOMIC IONS
AZOLES
BARYONS
CARBOXYLIC ACIDS
CHARGED PARTICLES
ELEMENTARY PARTICLES
FERMIONS
HADRONS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
INDOLES
IONS
KINETICS
MICROORGANISMS
NUCLEONS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRROLES
REACTION KINETICS
550200* - Biochemistry