@article {876,
	title = {The effect of different metal cation binding on the proton pumping in bacteriorhodopsin},
	journal = {Israel journal of chemistry},
	volume = {35},
	year = {1995},
	pages = {465-474},
	publisher = {Weizmann},
	abstract = {The first section of this paper is a detailed summary of studies made by us and others on metal cations binding to deionized bacteriorhodopsin (dIbR) and its variants. Our studies include the luminescence experiments of Eu3+ binding to dIbR and potentiometric studies of Ca2+ binding to dIbR, to deionized bR mutants, to bacterioopsin, and to dIbR with its C-terminus removed. The results suggest the presence of two classes of binding sites, one class has two high-affinity constants, and one has one low-affinity constant. For Ca2+ binding, there is one metal cation in each of the two high-affinity sites which are coupled to the charged aspartates 85 and 212 (known to be in the retinal cavity) but not coupled to each other. The low-affinity class can accommodate 0-6 Ca2+ ions and most of them are bound to the surface. Mg2+ has a slightly smaller value for its binding constant to the highest-affinity site. Thus, one expects more Ca2+ than Mg2+ bound to the two high-affinity sites. In the second section, we summarize our recent study on the effect of metal cation charge density (Ca2+, Mg2+, Eu3+, Tb3+, Ho3+, Dy3+) on the kinetics of both Schiff base deprotonation and proton transport to the extracellular surface. For all metal cations, the apparent rate constant of the slow components of the deprotonation process is the same as that for the transport process at 22 degrees C. The temperature studies, however, show this apparent equality to be fortuitous and to result from cancellation of the contribution of the energy and entropy of activation. Thus, while the entropy of activation is positive for the deprotonation process, it is negative for the proton transport process. These kinetic parameters depend weakly on the charge density, but in an opposite sense for the two processes. These results suggest that the deprotonation is not the rate-limiting step for the proton transport process. A possible mechanism is proposed in which a hydrated metal cation is used to induce the deprotonation of the protonated Schiff base and to dissociate one of its H2O molecules to donate the proton in the L-->M process.},
	isbn = {0021-2148},
	author = {El-Sayed, Mostafa A and Yang, Difei and Yoo, Seoung-Kyo and Zhang, N.}
}
@article {1284,
	title = {Fourier-transform infrared spectroscopic comparison of cultured human fibroblast and fibrosarcoma cells},
	journal = {Proceedings of SPIE},
	volume = {2389},
	year = {1995},
	month = {1995},
	pages = {543},
	publisher = {SPIE},
	abstract = {Infrared vibration spectroscopy appears to be a more powerful technique for diagnosis than visible or UV spectroscopy. Advantages of IR spectra include: 1) vibrational motion has a smaller tissue absorption coefficient than electronic motion, 2) scattering of infrared radiation has a lower cross section than visible or UV light, (these two facts allow deeper penetration of IR radiation) and 3) vibration spectra provide a better fingerprint of chemical groups present in cells than the unresolved broad electronic spectrum of biological molecules. In the present work, Fourier-transform IR spectroscopy was used to compare cultured human fibroblast and malignant fibrosarcoma cells. Significant differences were observed by comparing the spectra of the normal cells with that of the cancer cells. the PO2 symmetric stretching mode at 1082cm-1 in the cancer cell is reduced in intensity. These observations are similar to those reported previously by Wong et al in comparing the IR spectra of pairs of normal and cancerous cells from the colon and cervix. However, the observed increase in the relative intensity of the symmetric to antisymmetric CH3 bending mode are only found in fibrosarcoma and basal cell carcinoma. The decrease in intensity of the CH2 bending mode relative to that of CH3 mode was observed only for fibrosarcoma cells. This finding with paired human fibroblast and fibrosarcoma cells suggests that fatty acid chains or side chains of protein in the cancer cells are partially degraded leading to more terminal carbon. It is also possible that changes in the environment upon carcinogenesis induces a change in the relative absorption cross sections for the CH3 and CH2 bending vibrations.
},
	doi = {10.1117/12.210030},
	url = {http://dx.doi.org/10.1117/12.210030},
	author = {Yang, Difei},
	editor = {Castro, D. and El Sayed, I.H. and El-Sayed, Mostafa A and Saxton, R. and Zhang, N.}
}
@article {1283,
	title = {On the molecular mechanisms of the rapid and slow solar-to-electric energy storage processes by the other natural photosynthetic system, bacteriorhodopsin},
	journal = {Pure and applied chemistry},
	volume = {67},
	year = {1995},
	pages = {149-149},
	publisher = {BLACKWELL SCIENTIFIC PUBLICATIONS},
	abstract = {Upon the absorption of solar energy by retinal in bacterioi..>dopsin highly specific photoisomerization of the retinal around the C13 -C14 bond takes place. This is followed by the formation of a number of intermediates resulting from conformational changes of the protein around the retinal which leads to the deprotonation of the protonated Schiff base of the retinylidene system. Thisis the switch of the proton pump which leads to the last step in the storage of solar energy in the form of electric energy by this photosynthetic system. The removal of metal cations from bR is found to inhibit the deprotonation process.
In the present paper we summarize the results of our studies and the others regarding two important questions in the conversion process: 1) what is(are) the molecular mechanism(s) of the protein catalysis of the photoisomerizationprocess and 2) what is the role of metal cations in the deprotonation process of the protonated Schiff base (the switch of the proton pump)? In order to answer the first question, the results of the subpicosecondphotoisomerization rate of retinal in bR and in a number of its relevant mutants are discussed in terms of the steric and electronic factors. In an effort to answer the second question,we discussed the results of the binding studies of Ca*+to bR, to its mutants and to bR after its C- terminus is cleaved. From these results and the results of Roux et al. on the 31P NMR of Nd3+ regenerated bR, we concluded that one or two metal cations strongly bound to the protein but not on the surface, are functionally important. The model in which these metal cation@)control the pK values of Aspartic acids in the 85 and 212 positions and that of the protonated Schiff base (PSB) during the photocycle is discussed.},
	isbn = {0033-4545},
	author = {El-Sayed, Mostafa A and Griffiths, Jennifer A. and Song, Li and Zhang, N.}
}
