Temperature dependence cytochrome oxidation rate

Devault, D., and Chance, B., 1966, Studies of photosynthesis using a pulsed laser 1. Temperature dependence of cytochrome oxidation rate in chromatium. Evidence for Tunneling Biophysical J. 6 825n847. 

Figure 4. Temperature dependence of the rate constant for electron transfer from cytochrome < to the oxidized special pair in the reaction center of photosynthesis 11.3, 14. ...

Fig. 6. Temperature dependence of the rates of cytochrome oxidation in Chromatium ceils induced by 10-ns ( ) and 0.5-ms ( ) laser flashes. The numbers beside the data points are the number of observations averaged into one data point. Reproduced from DeVault and Chance (1966) On the kinetics and quantum efficiency of the chlorophyll-cytochrome reaction. Biophys J 6 832.

In some early studies of cytochrome reactions in photosynthetic bacteria. Chance and Nishimura made a remarkable observation with regard to the temperature dependence of photooxidation of the c-type cytochromes in photosynthetic bacteria. They found that in Chromatium the low-potential Cyt c553 (also called Cyt c423.5 according to the wavelength of the Soret band) can still undergo photooxidation at low temperatures. Fig. 5 shows that the oxidation rate of Chromatium Cyt c is about the same at 300 as at 250 K, while the rate of re-reduction is deaeased about 6-fold. What is remarkable is that at 77 K the rate of cytochrome oxidation appears to be even faster than at ambient temperature. The oxidized... 

The dependences, such as Eq. 2.47, are known as compensation effect, and coefficient (3C is denoted as isokinetic temperature at which all reactions of given series have the same rate constant. An example of compensation effect for for catalytic rate constant of the Sulfolobus solfataricus p-glycosidase reaction with different substrates is shown in Fig. 2.19. Similar relationships were reported for many other prosesses, involving the binding ligands to hemoglobin, the oxidation of alcohols by catalase, the hydroxylation of substrates by cytochrome c, etc. 

---