Conformational changes in bacteriorhodopsin accompanying ionophore activity
We conclude from planar membrane and liposome studies with bacteriorhodopsin in purple membrane fragments that 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 + +/, and by applied electric fields. The effect of bivalent ions appears to be two-fold, a direct effect on BR 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. Polymer stabilized black lipid membranes will prove quite useful for extending this test system for the study of ionophore activity of biological catalysts. Bacteriorhodopsin in the purple membrane patch exhibits considerable thermal stability and this intrinsic stability is enhanced by treatment with bifunctional crosslinking reagents. After chemical modification of bacteriorhodopsin in the light- or dark-adapted state, differences in proton pump activity are found in BR liposomes (which 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. Studies with bifunctional crosslinking 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:
- California Univ., Berkeley (USA). Lawrence Berkeley Lab.
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 5335668
- Report Number(s):
- LBL-6389; CONF-7606166-1
- Resource Relation:
- Conference: 67. annual meeting of the American Society of Biological Chemists, San Francisco, CA, USA, 6 Jun 1976
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
MEMBRANES
BIOCHEMICAL REACTION KINETICS
PIGMENTS
STRUCTURAL CHEMICAL ANALYSIS
BACTERIA
CATIONS
CONFIGURATION INTERACTION
ELECTRIC FIELDS
IONS
METABOLISM
PROTONS
BARYONS
CHARGED PARTICLES
ELEMENTARY PARTICLES
FERMIONS
HADRONS
KINETICS
MICROORGANISMS
NUCLEONS
REACTION KINETICS
550200* - Biochemistry
550500 - Metabolism