Requirement of water for anesthetic action: purple membrane
Bacteriorhodopsin (bR) in the purple membrane of Halobacterium salinarium is a retinal-containing protein. This chromophore changes color according to the state of the protein. The dark-adapted membranes, suspended in water, show the absorbance peak ( λ max) at 560 nm. Clinical concentrations of vol...
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| Published in: | Colloids and surfaces, B, Biointerfaces Vol. 13; no. 4; pp. 213 - 218 |
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| Main Authors: | , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
Elsevier B.V
01-05-1999
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| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Bacteriorhodopsin (bR) in the purple membrane of
Halobacterium salinarium is a retinal-containing protein. This chromophore changes color according to the state of the protein. The dark-adapted membranes, suspended in water, show the absorbance peak (
λ
max) at 560 nm. Clinical concentrations of volatile anesthetics, halothane, and enflurane, reversibly shifted
λ
max to 480 nm. When dried membranes were dispersed water-free liquid anesthetics, these spectral changes were not observed. Addition of water shifted
λ
max to 480 nm. The [H
2O/bR] mole ratio that was necessary to induce the full spectral change was about 3000 for halothane and 20 000 for enflurane. Addition of water would decrease the interfacial energy between the hydrophilic purple membrane and the hydrophobic anesthetics. The water-induced interaction between purple membrane and anesthetics is attributable to the positive spreading coefficient of water at the anesthetic/membrane interface,
S
water(anes/memb), expressed as
S
water(
anes/
memb)
=γ
memb/
anes
−γ
memb/
water
−γ
water/
anes
where
γ
memb/anes,
γ
memb/water, and
γ
water/anes represent in the interfacial tension between membrane/anesthetic, membrane/water, and water/anesthetic phases, respectively. The surface energy of water is 72.8 mJ m
−2 (20°C) and consists of polarity (50.8 mJ m
−2), and dispersibility (22.0 mJ m
−2). The polarity of water contributes to the interaction with the polar surface of purple membrane, and the dispersibility contributes to the interaction with hydrophobic anesthetics. The amphiphilicity of water molecules is the principal factor to decrease the interfacial energy between membrane and anesthetic molecules. The present result shows that anesthetic interaction with biological phase requires water. |
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| ISSN: | 0927-7765 1873-4367 |
| DOI: | 10.1016/S0927-7765(99)00007-7 |