Comparison between the binding of Ca{sup 2+} and Mg{sup 2+} to the two high-affinity sites of bacteriorhodopsin
- Georgia Inst. of Technology, Atlanta, GA (United States)
Bacteriorhodopsin contains Ca{sup 2+} and Mg{sup 2+} ions whose removal inhibits its proton pump function. The binding constants of Ca{sup 2+} to the high-affinity sites were determined by the use of a calcium ion specific electrode. The unavailability of magnesium ion specific electrode prevented a similar determination for Mg{sup 2+}. The binding constant of Mg{sup 2+} to the binding site of highest affinity is determined by using a calcium ion selective electrode to measure the concentration of free Ca{sup 2+} in competition with Mg{sup 2+} for the binding. The binding constant of Mg{sup 2+} to the second high affinity site is determined spectrally. The two high-affinity binding constants for Mg{sup 2+} are compared with those obtained for Ca{sup 2+} in the absence and the presence of Mg{sup 2+}. The fact that the presence of low concentration of one metal ion does not affect the binding constant of the other metal ion to the other binding site supports the assumption of the independence of the two high-affinity sites of one another. The difference in the observed values of the binding constants of the two high-affinity sites for Ca{sup 2+} and Mg{sup 2+} is qualitatively discussed in terms of the enthalpy and entropy changes in the binding equilibrium. 51 refs., 3 figs., 2 tabs.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FG03-88ER13828
- OSTI ID:
- 91258
- Journal Information:
- Journal of Physical Chemistry, Vol. 99, Issue 29; Other Information: PBD: 20 Jul 1995
- Country of Publication:
- United States
- Language:
- English
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