Abstract
The volume and enthalpy changes associated with proton translocation steps during the bacteriorhodopsin (BR) photocycle were determined by time-resolved photopressure measurements. The data at 25°C show a prompt increase in volume followed by two further increases and one decrease to the original state to complete the cycle. These volume changes are decomposed into enthalpy and inherent volume changes. The positive enthalpy changes support the argument for inherent entropy-driven late steps in the BR photocycle [Ort, D. R., and Parson, W. M. (1979) Enthalpy changes during the photochemical cycle of bacteriorhodopsin. Biophys. J. 25, 355-364]. The volume change data can be interpreted by the electrostriction effect as charges are canceled and formed during the proton transfers. A simple glutamic acid-glutamate ion model or a diglutamate-arginine-protonated water charge-delocalized model for the proton-release complex (PRC) fit the data. A conformational change with a large positive volume change is required in the slower rise (M → N of the optical cycle) step and is reversed in the decay (N → O → BR) steps. The large variation in the published values for both the volume and enthalpy changes is greatly ameliorated if the values are presented per absorbed photon instead of per mole of BR. Thus, it is the highly differing assumptions about the quantum or reaction yields that cause the variations in the published results.
| Original language | English |
|---|---|
| Pages (from-to) | 7752-7761 |
| Number of pages | 10 |
| Journal | Biochemistry |
| Volume | 47 |
| Issue number | 29 |
| DOIs | |
| Publication status | Published - Jul 22 2008 |
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- Biochemistry
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Volume and enthalpy changes of proton transfers in the bacteriorhodopsin photocycle studied by millisecond time-resolved photopressure measurements. / Liu, Yan; Edens, Gregory J.; Grzymski, Joseph; Mauzerall, David.
In: Biochemistry, Vol. 47, No. 29, 22.07.2008, p. 7752-7761.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Volume and enthalpy changes of proton transfers in the bacteriorhodopsin photocycle studied by millisecond time-resolved photopressure measurements
AU - Liu, Yan
AU - Edens, Gregory J.
AU - Grzymski, Joseph
AU - Mauzerall, David
PY - 2008/7/22
Y1 - 2008/7/22
N2 - The volume and enthalpy changes associated with proton translocation steps during the bacteriorhodopsin (BR) photocycle were determined by time-resolved photopressure measurements. The data at 25°C show a prompt increase in volume followed by two further increases and one decrease to the original state to complete the cycle. These volume changes are decomposed into enthalpy and inherent volume changes. The positive enthalpy changes support the argument for inherent entropy-driven late steps in the BR photocycle [Ort, D. R., and Parson, W. M. (1979) Enthalpy changes during the photochemical cycle of bacteriorhodopsin. Biophys. J. 25, 355-364]. The volume change data can be interpreted by the electrostriction effect as charges are canceled and formed during the proton transfers. A simple glutamic acid-glutamate ion model or a diglutamate-arginine-protonated water charge-delocalized model for the proton-release complex (PRC) fit the data. A conformational change with a large positive volume change is required in the slower rise (M → N of the optical cycle) step and is reversed in the decay (N → O → BR) steps. The large variation in the published values for both the volume and enthalpy changes is greatly ameliorated if the values are presented per absorbed photon instead of per mole of BR. Thus, it is the highly differing assumptions about the quantum or reaction yields that cause the variations in the published results.
AB - The volume and enthalpy changes associated with proton translocation steps during the bacteriorhodopsin (BR) photocycle were determined by time-resolved photopressure measurements. The data at 25°C show a prompt increase in volume followed by two further increases and one decrease to the original state to complete the cycle. These volume changes are decomposed into enthalpy and inherent volume changes. The positive enthalpy changes support the argument for inherent entropy-driven late steps in the BR photocycle [Ort, D. R., and Parson, W. M. (1979) Enthalpy changes during the photochemical cycle of bacteriorhodopsin. Biophys. J. 25, 355-364]. The volume change data can be interpreted by the electrostriction effect as charges are canceled and formed during the proton transfers. A simple glutamic acid-glutamate ion model or a diglutamate-arginine-protonated water charge-delocalized model for the proton-release complex (PRC) fit the data. A conformational change with a large positive volume change is required in the slower rise (M → N of the optical cycle) step and is reversed in the decay (N → O → BR) steps. The large variation in the published values for both the volume and enthalpy changes is greatly ameliorated if the values are presented per absorbed photon instead of per mole of BR. Thus, it is the highly differing assumptions about the quantum or reaction yields that cause the variations in the published results.
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U2 - 10.1021/bi800158x
DO - 10.1021/bi800158x
M3 - Article
VL - 47
SP - 7752
EP - 7761
JO - Biochemistry
JF - Biochemistry
SN - 0006-2960
IS - 29
ER -