Skip to main content
NCBI home page
Biophysical Journal logoLink to Biophysical Journal
. 2001 Feb;80(2):961–971. doi: 10.1016/S0006-3495(01)76075-4

Time-resolved Fourier transform infrared spectroscopy of the polarizable proton continua and the proton pump mechanism of bacteriorhodopsin.

J Wang 1, M A El-Sayed 1
PMCID: PMC1301294  PMID: 11159463

Abstract

Nanosecond-to-microsecond time-resolved Fourier transform infrared (FTIR) spectroscopy in the 3000-1000-cm(-1) region has been used to examine the polarizable proton continua observed in bacteriorhodopsin (bR) during its photocycle. The difference in the transient FTIR spectra in the time domain between 20 ns and 1 ms shows a broad absorption continuum band in the 2100-1800-cm(-1) region, a bleach continuum band in the 2500-2150-cm(-1) region, and a bleach continuum band above 2700 cm(-1). According to Zundel (G., J. Mol. Struct. 322:33-42), these continua appear in systems capable of forming polarizable hydrogen bonds. The formation of a bleach continuum suggests the presence of a polarizable proton in the ground state that changes during the photocycle. The appearance of a transient absorption continuum suggests a change in the polarizable proton or the appearance of new ones. It is found that each continuum has a rise time of less than 80 ns and a decay time component of approximately 300 micros. In addition, it is found that the absorption continuum in the 2100-1800-cm(-1) region has a slow rise component of 190 ns and a fast decay component of approximately 60 micros. Using these results and those of the recent x-ray structural studies of bR(570) and M(412) (H. Luecke, B. Schobert, H.T. Richter, J.-P. Cartailler, and J. K., Science 286:255-260), together with the already known spectroscopic properties of the different intermediates in the photocycle, the possible origins of the polarizable protons giving rise to these continua during the bR photocycle are proposed. Models of the proton pump are discussed in terms of the changes in these polarizable protons and the hydrogen-bonded chains and in terms of previously known results such as the simultaneous deprotonation of the protonated Schiff base (PSB) and Tyr185 and the disappearance of water molecules in the proton release channel during the proton pump process.

Full Text

The Full Text of this article is available as a PDF (137.7 KB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Alexiev U., Mollaaghababa R., Scherrer P., Khorana H. G., Heyn M. P. Rapid long-range proton diffusion along the surface of the purple membrane and delayed proton transfer into the bulk. Proc Natl Acad Sci U S A. 1995 Jan 17;92(2):372–376. doi: 10.1073/pnas.92.2.372. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Ariki M., Lanyi J. K. Characterization of metal ion-binding sites in bacteriorhodopsin. J Biol Chem. 1986 Jun 25;261(18):8167–8174. [PubMed] [Google Scholar]
  3. Balashov S. P., Govindjee R., Imasheva E. S., Misra S., Ebrey T. G., Feng Y., Crouch R. K., Menick D. R. The two pKa's of aspartate-85 and control of thermal isomerization and proton release in the arginine-82 to lysine mutant of bacteriorhodopsin. Biochemistry. 1995 Jul 11;34(27):8820–8834. doi: 10.1021/bi00027a034. [DOI] [PubMed] [Google Scholar]
  4. Balashov S. P., Govindjee R., Kono M., Imasheva E., Lukashev E., Ebrey T. G., Crouch R. K., Menick D. R., Feng Y. Effect of the arginine-82 to alanine mutation in bacteriorhodopsin on dark adaptation, proton release, and the photochemical cycle. Biochemistry. 1993 Oct 5;32(39):10331–10343. doi: 10.1021/bi00090a008. [DOI] [PubMed] [Google Scholar]
  5. Birge R. R. Photophysics of light transduction in rhodopsin and bacteriorhodopsin. Annu Rev Biophys Bioeng. 1981;10:315–354. doi: 10.1146/annurev.bb.10.060181.001531. [DOI] [PubMed] [Google Scholar]
  6. Bousché O., Sonar S., Krebs M. P., Khorana H. G., Rothschild K. J. Time-resolved Fourier transform infrared spectroscopy of the bacteriorhodopsin mutant Tyr-185-->Phe: Asp-96 reprotonates during O formation; Asp-85 and Asp-212 deprotonate during O decay. Photochem Photobiol. 1992 Dec;56(6):1085–1095. doi: 10.1111/j.1751-1097.1992.tb09732.x. [DOI] [PubMed] [Google Scholar]
  7. Braiman M. S., Mogi T., Marti T., Stern L. J., Khorana H. G., Rothschild K. J. Vibrational spectroscopy of bacteriorhodopsin mutants: light-driven proton transport involves protonation changes of aspartic acid residues 85, 96, and 212. Biochemistry. 1988 Nov 15;27(23):8516–8520. doi: 10.1021/bi00423a002. [DOI] [PubMed] [Google Scholar]
  8. Brown L. S., Needleman R., Lanyi J. K. Interaction of proton and chloride transfer pathways in recombinant bacteriorhodopsin with chloride transport activity: implications for the chloride translocation mechanism. Biochemistry. 1996 Dec 17;35(50):16048–16054. doi: 10.1021/bi9622938. [DOI] [PubMed] [Google Scholar]
  9. Brown L. S., Sasaki J., Kandori H., Maeda A., Needleman R., Lanyi J. K. Glutamic acid 204 is the terminal proton release group at the extracellular surface of bacteriorhodopsin. J Biol Chem. 1995 Nov 10;270(45):27122–27126. doi: 10.1074/jbc.270.45.27122. [DOI] [PubMed] [Google Scholar]
  10. Chang C. H., Chen J. G., Govindjee R., Ebrey T. Cation binding by bacteriorhodopsin. Proc Natl Acad Sci U S A. 1985 Jan;82(2):396–400. doi: 10.1073/pnas.82.2.396. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Chang C. W., Sekiya N., Yoshihara K. O-H stretching vibration in Fourier transform difference infrared spectra of bacteriorhodopsin. FEBS Lett. 1991 Aug 5;287(1-2):157–159. doi: 10.1016/0014-5793(91)80039-6. [DOI] [PubMed] [Google Scholar]
  12. Chronister E. L., Corcoran T. C., Song L., El-Sayed M. A. On the molecular mechanisms of the Schiff base deprotonation during the bacteriorhodopsin photocycle. Proc Natl Acad Sci U S A. 1986 Nov;83(22):8580–8584. doi: 10.1073/pnas.83.22.8580. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Corcoran T. C., Ismail K. Z., El-Sayed M. A. Evidence for the involvement of more than one metal cation in the Schiff base deprotonation process during the photocycle of bacteriorhodopsin. Proc Natl Acad Sci U S A. 1987 Jun;84(12):4094–4098. doi: 10.1073/pnas.84.12.4094. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Dencher N. A., Papadopoulos G., Dresselhaus D., Büldt G. Light- and dark-adapted bacteriorhodopsin, a time-resolved neutron diffraction study. Biochim Biophys Acta. 1990 Jul 9;1026(1):51–56. doi: 10.1016/0005-2736(90)90331-h. [DOI] [PubMed] [Google Scholar]
  15. Deng H., Huang L., Callender R., Ebrey T. Evidence for a bound water molecule next to the retinal Schiff base in bacteriorhodopsin and rhodopsin: a resonance Raman study of the Schiff base hydrogen/deuterium exchange. Biophys J. 1994 Apr;66(4):1129–1136. doi: 10.1016/S0006-3495(94)80893-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Dioumaev A. K., Richter H. T., Brown L. S., Tanio M., Tuzi S., Saito H., Kimura Y., Needleman R., Lanyi J. K. Existence of a proton transfer chain in bacteriorhodopsin: participation of Glu-194 in the release of protons to the extracellular surface. Biochemistry. 1998 Feb 24;37(8):2496–2506. doi: 10.1021/bi971842m. [DOI] [PubMed] [Google Scholar]
  17. Dupuis P., Corcoran T. C., El-Sayed M. A. Importance of bound divalent cations to the tyrosine deprotonation during the photocycle of bacteriorhodopsin. Proc Natl Acad Sci U S A. 1985 Jun;82(11):3662–3664. doi: 10.1073/pnas.82.11.3662. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Duñach M., Berkowitz S., Marti T., He Y. W., Subramaniam S., Khorana H. G., Rothschild K. J. Ultraviolet-visible transient spectroscopy of bacteriorhodopsin mutants. Evidence for two forms of tyrosine-185----phenylalanine. J Biol Chem. 1990 Oct 5;265(28):16978–16984. [PubMed] [Google Scholar]
  19. Earnest T. N., Roepe P., Braiman M. S., Gillespie J., Rothschild K. J. Orientation of the bacteriorhodopsin chromophore probed by polarized Fourier transform infrared difference spectroscopy. Biochemistry. 1986 Dec 2;25(24):7793–7798. doi: 10.1021/bi00372a002. [DOI] [PubMed] [Google Scholar]
  20. Edman K., Nollert P., Royant A., Belrhali H., Pebay-Peyroula E., Hajdu J., Neutze R., Landau E. M. High-resolution X-ray structure of an early intermediate in the bacteriorhodopsin photocycle. Nature. 1999 Oct 21;401(6755):822–826. doi: 10.1038/44623. [DOI] [PubMed] [Google Scholar]
  21. Essen L., Siegert R., Lehmann W. D., Oesterhelt D. Lipid patches in membrane protein oligomers: crystal structure of the bacteriorhodopsin-lipid complex. Proc Natl Acad Sci U S A. 1998 Sep 29;95(20):11673–11678. doi: 10.1073/pnas.95.20.11673. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Fischer W. B., Sonar S., Marti T., Khorana H. G., Rothschild K. J. Detection of a water molecule in the active-site of bacteriorhodopsin: hydrogen bonding changes during the primary photoreaction. Biochemistry. 1994 Nov 1;33(43):12757–12762. doi: 10.1021/bi00209a005. [DOI] [PubMed] [Google Scholar]
  23. Fu X., Bressler S., Ottolenghi M., Eliash T., Friedman N., Sheves M. Titration kinetics of Asp-85 in bacteriorhodopsin: exclusion of the retinal pocket as the color-controlling cation binding site. FEBS Lett. 1997 Oct 20;416(2):167–170. doi: 10.1016/s0014-5793(97)01194-0. [DOI] [PubMed] [Google Scholar]
  24. Govindjee R., Misra S., Balashov S. P., Ebrey T. G., Crouch R. K., Menick D. R. Arginine-82 regulates the pKa of the group responsible for the light-driven proton release in bacteriorhodopsin. Biophys J. 1996 Aug;71(2):1011–1023. doi: 10.1016/S0006-3495(96)79302-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Heberle J., Dencher N. A. Bacteriorhodopsin in ice. Accelerated proton transfer from the purple membrane surface. FEBS Lett. 1990 Dec 17;277(1-2):277–280. doi: 10.1016/0014-5793(90)80864-f. [DOI] [PubMed] [Google Scholar]
  26. Heberle J., Dencher N. A. Surface-bound optical probes monitor protein translocation and surface potential changes during the bacteriorhodopsin photocycle. Proc Natl Acad Sci U S A. 1992 Jul 1;89(13):5996–6000. doi: 10.1073/pnas.89.13.5996. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Heberle J., Oesterhelt D., Dencher N. A. Decoupling of photo- and proton cycle in the Asp85-->Glu mutant of bacteriorhodopsin. EMBO J. 1993 Oct;12(10):3721–3727. doi: 10.1002/j.1460-2075.1993.tb06049.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Henderson R., Baldwin J. M., Ceska T. A., Zemlin F., Beckmann E., Downing K. H. Model for the structure of bacteriorhodopsin based on high-resolution electron cryo-microscopy. J Mol Biol. 1990 Jun 20;213(4):899–929. doi: 10.1016/S0022-2836(05)80271-2. [DOI] [PubMed] [Google Scholar]
  29. Henderson R. The structure of bacteriorhodopsin and its relevance to other membrane proteins. Soc Gen Physiol Ser. 1979;33:3–15. [PubMed] [Google Scholar]
  30. Jonas R., Koutalos Y., Ebrey T. G. Purple membrane: surface charge density and the multiple effect of pH and cations. Photochem Photobiol. 1990 Dec;52(6):1163–1177. doi: 10.1111/j.1751-1097.1990.tb08455.x. [DOI] [PubMed] [Google Scholar]
  31. Kandori H., Yamazaki Y., Hatanaka M., Needleman R., Brown L. S., Richter H. T., Lanyi J. K., Maeda A. Time-resolved fourier transform infrared study of structural changes in the last steps of the photocycles of Glu-204 and Leu-93 mutants of bacteriorhodopsin. Biochemistry. 1997 Apr 29;36(17):5134–5141. doi: 10.1021/bi9629788. [DOI] [PubMed] [Google Scholar]
  32. Keszthelyi L., Ormos P. Displacement current on purple membrane fragments oriented in a suspension. Biophys Chem. 1983 Nov;18(4):397–405. doi: 10.1016/0301-4622(83)80053-2. [DOI] [PubMed] [Google Scholar]
  33. Koch M. H., Dencher N. A., Oesterhelt D., Plöhn H. J., Rapp G., Büldt G. Time-resolved X-ray diffraction study of structural changes associated with the photocycle of bacteriorhodopsin. EMBO J. 1991 Mar;10(3):521–526. doi: 10.1002/j.1460-2075.1991.tb07978.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Lam E., Seltzer S., Katsura T., Packer L. Light-dependent nitration of bacteriorhodopsin. Arch Biochem Biophys. 1983 Nov;227(1):321–328. doi: 10.1016/0003-9861(83)90376-4. [DOI] [PubMed] [Google Scholar]
  35. Lanyi J. K. Proton translocation mechanism and energetics in the light-driven pump bacteriorhodopsin. Biochim Biophys Acta. 1993 Dec 7;1183(2):241–261. doi: 10.1016/0005-2728(93)90226-6. [DOI] [PubMed] [Google Scholar]
  36. Lemke H. D., Oesterhelt D. The role of tyrosine residues in the function of bacteriorhodopsin. Specific nitration of tyrosine 26. Eur J Biochem. 1981 Apr;115(3):595–604. doi: 10.1111/j.1432-1033.1981.tb06244.x. [DOI] [PubMed] [Google Scholar]
  37. Liu S. Y., Ebrey T. G. Photocurrent measurements of the purple membrane oriented in a polyacrylamide gel. Biophys J. 1988 Aug;54(2):321–329. doi: 10.1016/S0006-3495(88)82962-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Liu S. Y. Light-induced currents from oriented purple membrane: I. Correlation of the microsecond component (B2) with the L-M photocycle transition. Biophys J. 1990 May;57(5):943–950. doi: 10.1016/S0006-3495(90)82614-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Lu M., Balashov S. P., Ebrey T. G., Chen N., Chen Y., Menick D. R., Crouch R. K. Evidence for the rate of the final step in the bacteriorhodopsin photocycle being controlled by the proton release group: R134H mutant. Biochemistry. 2000 Mar 7;39(9):2325–2331. doi: 10.1021/bi992554o. [DOI] [PubMed] [Google Scholar]
  40. Luecke H., Richter H. T., Lanyi J. K. Proton transfer pathways in bacteriorhodopsin at 2.3 angstrom resolution. Science. 1998 Jun 19;280(5371):1934–1937. doi: 10.1126/science.280.5371.1934. [DOI] [PubMed] [Google Scholar]
  41. Luecke H., Schobert B., Richter H. T., Cartailler J. P., Lanyi J. K. Structural changes in bacteriorhodopsin during ion transport at 2 angstrom resolution. Science. 1999 Oct 8;286(5438):255–261. doi: 10.1126/science.286.5438.255. [DOI] [PubMed] [Google Scholar]
  42. Luecke H., Schobert B., Richter H. T., Cartailler J. P., Lanyi J. K. Structure of bacteriorhodopsin at 1.55 A resolution. J Mol Biol. 1999 Aug 27;291(4):899–911. doi: 10.1006/jmbi.1999.3027. [DOI] [PubMed] [Google Scholar]
  43. Lugtenburg J., Mathies R. A., Griffin R. G., Herzfeld J. Structure and function of rhodopsins from solid state NMR and resonance Raman spectroscopy of isotopic retinal derivatives. Trends Biochem Sci. 1988 Oct;13(10):388–393. doi: 10.1016/0968-0004(88)90181-8. [DOI] [PubMed] [Google Scholar]
  44. Maeda A., Sasaki J., Shichida Y., Yoshizawa T. Water structural changes in the bacteriorhodopsin photocycle: analysis by Fourier transform infrared spectroscopy. Biochemistry. 1992 Jan 21;31(2):462–467. doi: 10.1021/bi00117a023. [DOI] [PubMed] [Google Scholar]
  45. Mathies R. A., Brito Cruz C. H., Pollard W. T., Shank C. V. Direct observation of the femtosecond excited-state cis-trans isomerization in bacteriorhodopsin. Science. 1988 May 6;240(4853):777–779. doi: 10.1126/science.3363359. [DOI] [PubMed] [Google Scholar]
  46. Mathies R. A., Lin S. W., Ames J. B., Pollard W. T. From femtoseconds to biology: mechanism of bacteriorhodopsin's light-driven proton pump. Annu Rev Biophys Biophys Chem. 1991;20:491–518. doi: 10.1146/annurev.bb.20.060191.002423. [DOI] [PubMed] [Google Scholar]
  47. Merz H., Zundel G. Thermodynamics of proton transfer in carboxylic acid-retinal Schiff base hydrogen bonds with large proton polarizability. Biochem Biophys Res Commun. 1986 Jul 31;138(2):819–825. doi: 10.1016/s0006-291x(86)80570-8. [DOI] [PubMed] [Google Scholar]
  48. Misra S., Govindjee R., Ebrey T. G., Chen N., Ma J. X., Crouch R. K. Proton uptake and release are rate-limiting steps in the photocycle of the bacteriorhodopsin mutant E204Q. Biochemistry. 1997 Apr 22;36(16):4875–4883. doi: 10.1021/bi962673t. [DOI] [PubMed] [Google Scholar]
  49. Mitra A. K., Stroud R. M. High sensitivity electron diffraction analysis. A study of divalent cation binding to purple membrane. Biophys J. 1990 Feb;57(2):301–311. doi: 10.1016/S0006-3495(90)82532-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  50. Nilsson A., Rath P., Olejnik J., Coleman M., Rothschild K. J. Protein conformational changes during the bacteriorhodopsin photocycle. A Fourier transform infrared/resonance Raman study of the alkaline form of the mutant Asp-85-->Asn. J Biol Chem. 1995 Dec 15;270(50):29746–29751. doi: 10.1074/jbc.270.50.29746. [DOI] [PubMed] [Google Scholar]
  51. Oka T., Kamikubo H., Tokunaga F., Lanyi J. K., Needleman R., Kataoka M. Conformational change of helix G in the bacteriorhodopsin photocycle: investigation with heavy atom labeling and x-ray diffraction. Biophys J. 1999 Feb;76(2):1018–1023. doi: 10.1016/S0006-3495(99)77266-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  52. Otto H., Marti T., Holz M., Mogi T., Stern L. J., Engel F., Khorana H. G., Heyn M. P. Substitution of amino acids Asp-85, Asp-212, and Arg-82 in bacteriorhodopsin affects the proton release phase of the pump and the pK of the Schiff base. Proc Natl Acad Sci U S A. 1990 Feb;87(3):1018–1022. doi: 10.1073/pnas.87.3.1018. [DOI] [PMC free article] [PubMed] [Google Scholar]
  53. Papadopoulos G., Dencher N. A., Zaccai G., Büldt G. Water molecules and exchangeable hydrogen ions at the active centre of bacteriorhodopsin localized by neutron diffraction. Elements of the proton pathway? J Mol Biol. 1990 Jul 5;214(1):15–19. doi: 10.1016/0022-2836(90)90140-h. [DOI] [PubMed] [Google Scholar]
  54. Pardo L., Sepulcre F., Cladera J., Duñach M., Labarta A., Tejada J., Padrós E. Experimental and theoretical characterization of the high-affinity cation-binding site of the purple membrane. Biophys J. 1998 Aug;75(2):777–784. doi: 10.1016/S0006-3495(98)77567-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  55. Pebay-Peyroula E., Rummel G., Rosenbusch J. P., Landau E. M. X-ray structure of bacteriorhodopsin at 2.5 angstroms from microcrystals grown in lipidic cubic phases. Science. 1997 Sep 12;277(5332):1676–1681. doi: 10.1126/science.277.5332.1676. [DOI] [PubMed] [Google Scholar]
  56. Rammelsberg R., Huhn G., Lübben M., Gerwert K. Bacteriorhodopsin's intramolecular proton-release pathway consists of a hydrogen-bonded network. Biochemistry. 1998 Apr 7;37(14):5001–5009. doi: 10.1021/bi971701k. [DOI] [PubMed] [Google Scholar]
  57. Richter H. T., Brown L. S., Needleman R., Lanyi J. K. A linkage of the pKa's of asp-85 and glu-204 forms part of the reprotonation switch of bacteriorhodopsin. Biochemistry. 1996 Apr 2;35(13):4054–4062. doi: 10.1021/bi952883q. [DOI] [PubMed] [Google Scholar]
  58. Riesle J., Oesterhelt D., Dencher N. A., Heberle J. D38 is an essential part of the proton translocation pathway in bacteriorhodopsin. Biochemistry. 1996 May 28;35(21):6635–6643. doi: 10.1021/bi9600456. [DOI] [PubMed] [Google Scholar]
  59. Rothschild K. J., Braiman M. S., He Y. W., Marti T., Khorana H. G. Vibrational spectroscopy of bacteriorhodopsin mutants. Evidence for the interaction of aspartic acid 212 with tyrosine 185 and possible role in the proton pump mechanism. J Biol Chem. 1990 Oct 5;265(28):16985–16991. [PubMed] [Google Scholar]
  60. Rothschild K. J. FTIR difference spectroscopy of bacteriorhodopsin: toward a molecular model. J Bioenerg Biomembr. 1992 Apr;24(2):147–167. doi: 10.1007/BF00762674. [DOI] [PubMed] [Google Scholar]
  61. Rothschild K. J., He Y. W., Mogi T., Marti T., Stern L. J., Khorana H. G. Vibrational spectroscopy of bacteriorhodopsin mutants: evidence for the interaction of proline-186 with the retinylidene chromophore. Biochemistry. 1990 Jun 26;29(25):5954–5960. doi: 10.1021/bi00477a011. [DOI] [PubMed] [Google Scholar]
  62. Sasaki J., Maeda A., Kato C., Hamaguchi H. Time-resolved infrared spectral analysis of the KL-to-L conversion in the photocycle of bacteriorhodopsin. Biochemistry. 1993 Jan 26;32(3):867–871. doi: 10.1021/bi00054a018. [DOI] [PubMed] [Google Scholar]
  63. Scherrer P., Packer L., Seltzer S. Effect of iodination of the purple membrane on the photocycle of bacteriorhodopsin. Arch Biochem Biophys. 1981 Dec;212(2):589–601. doi: 10.1016/0003-9861(81)90402-1. [DOI] [PubMed] [Google Scholar]
  64. Smith S. O., Hornung I., van der Steen R., Pardoen J. A., Braiman M. S., Lugtenburg J., Mathies R. A. Are C14-C15 single bond isomerizations of the retinal chromophore involved in the proton-pumping mechanism of bacteriorhodopsin? Proc Natl Acad Sci U S A. 1986 Feb;83(4):967–971. doi: 10.1073/pnas.83.4.967. [DOI] [PMC free article] [PubMed] [Google Scholar]
  65. Souvignier G., Gerwert K. Proton uptake mechanism of bacteriorhodopsin as determined by time-resolved stroboscopic-FTIR-spectroscopy. Biophys J. 1992 Nov;63(5):1393–1405. doi: 10.1016/S0006-3495(92)81722-8. [DOI] [PMC free article] [PubMed] [Google Scholar]
  66. Stoeckenius W., Lozier R. H. Light energy conversion in Halobacterium halobium. J Supramol Struct. 1974;2(5-6):769–774. doi: 10.1002/jss.400020519. [DOI] [PubMed] [Google Scholar]
  67. Szundi I., Stoeckenius W. Effect of lipid surface charges on the purple-to-blue transition of bacteriorhodopsin. Proc Natl Acad Sci U S A. 1987 Jun;84(11):3681–3684. doi: 10.1073/pnas.84.11.3681. [DOI] [PMC free article] [PubMed] [Google Scholar]
  68. Szundi I., Stoeckenius W. Purple-to-blue transition of bacteriorhodopsin in a neutral lipid environment. Biophys J. 1988 Aug;54(2):227–232. doi: 10.1016/S0006-3495(88)82951-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  69. Szundi I., Stoeckenius W. Surface pH controls purple-to-blue transition of bacteriorhodopsin. A theoretical model of purple membrane surface. Biophys J. 1989 Aug;56(2):369–383. doi: 10.1016/S0006-3495(89)82683-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  70. Trissl H. W. Photoelectric measurements of purple membranes. Photochem Photobiol. 1990 Jun;51(6):793–818. [PubMed] [Google Scholar]
  71. Tuzi S., Yamaguchi S., Tanio M., Konishi H., Inoue S., Naito A., Needleman R., Lanyi J. K., Saitô H. Location of a cation-binding site in the loop between helices F and G of bacteriorhodopsin as studied by 13C NMR. Biophys J. 1999 Mar;76(3):1523–1531. doi: 10.1016/S0006-3495(99)77311-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  72. Váró G., Brown L. S., Needleman R., Lanyi J. K. Binding of calcium ions to bacteriorhodopsin. Biophys J. 1999 Jun;76(6):3219–3226. doi: 10.1016/S0006-3495(99)77473-4. [DOI] [PMC free article] [PubMed] [Google Scholar]
  73. Yang D., el-Sayed M. A. The Ca2+ binding to deionized monomerized and to retinal removed bacteriorhodopsin. Biophys J. 1995 Nov;69(5):2056–2059. doi: 10.1016/S0006-3495(95)80075-5. [DOI] [PMC free article] [PubMed] [Google Scholar]
  74. Zhang Y. N., Sweetman L. L., Awad E. S., El-Sayed M. A. Nature of the individual Ca binding sites in Ca-regenerated bacteriorhodopsin. Biophys J. 1992 May;61(5):1201–1206. doi: 10.1016/S0006-3495(92)81929-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  75. Zhang Y. N., el-Sayed M. A., Bonet M. L., Lanyi J. K., Chang M., Ni B., Needleman R. Effects of genetic replacements of charged and H-bonding residues in the retinal pocket on Ca2+ binding to deionized bacteriorhodopsin. Proc Natl Acad Sci U S A. 1993 Feb 15;90(4):1445–1449. doi: 10.1073/pnas.90.4.1445. [DOI] [PMC free article] [PubMed] [Google Scholar]
  76. Zscherp C., Schlesinger R., Tittor J., Oesterhelt D., Heberle J. In situ determination of transient pKa changes of internal amino acids of bacteriorhodopsin by using time-resolved attenuated total reflection Fourier-transform infrared spectroscopy. Proc Natl Acad Sci U S A. 1999 May 11;96(10):5498–5503. doi: 10.1073/pnas.96.10.5498. [DOI] [PMC free article] [PubMed] [Google Scholar]
  77. Zundel G., Merz H. On the role of hydrogen bonds and hydrogen-bonded systems with large proton polarizability for mechanisms of proton activation and conduction in bacteriorhodopsin. Prog Clin Biol Res. 1984;164:153–164. [PubMed] [Google Scholar]
  78. van den Berg R., Du-Jeon-Jang, Bitting H. C., El-Sayed M. A. Subpicosecond resonance Raman spectra of the early intermediates in the photocycle of bacteriorhodopsin. Biophys J. 1990 Jul;58(1):135–141. doi: 10.1016/S0006-3495(90)82359-6. [DOI] [PMC free article] [PubMed] [Google Scholar]

Articles from Biophysical Journal are provided here courtesy of The Biophysical Society

RESOURCES