J. Biol. Chem., Vol. 260, Issue 3, 1407-1412, 02, 1985
Reversible acidic-alkaline transition of the carbon monoxide complex of cytochrome c peroxidase
T Iizuka, R Makino, Y Ishimura and T Yonetani
The Soret absorption band of the ferrous carbon monoxide (CO) complex of
cytochrome c peroxidase exhibited a blue shift from 423.7 to 420 nm upon an
increase in pH from 6.5 to 8.5. The spectral change was reversible with an
isosbestic point at 422 nm. The pH dependence of this spectral change gave
a sigmoidal curve fitted well to a theoretical curve of a cooperative
release of two protons with a pK value of 7.5, indicating the existence of
the acidic and alkaline forms of the ferrous CO enzyme. Upon irradiation of
light flash (100 J of power and 30-microseconds), the heme-bound CO was
readily dissociated in both acidic and alkaline forms with a quantum yield
of approximately unity. On the other hand, the rate of recombination of the
dissociated CO with the heme iron was significantly different between these
two forms; the recombination rate constants were 1.1 X 10(3) and 3.0 X
10(4) M-1 S-1 at 25 degrees C for the acidic and alkaline forms,
respectively. At intermediate pH values, kinetics of recombination were
biphasic, consisting of the slow and fast processes with the appropriate
rate constants mentioned above. When the fraction of the fast process was
plotted against pH, the pH profile coincided with the spectrophotometric pH
titration curve described above. Thus, it was concluded that the acidic and
alkaline forms of the enzyme were responsible for the slow and fast
processes, respectively. In infrared spectroscopy, the acidic form showed a
narrow CO stretching band at 1922 cm-1 with a half-band width of 12.5 cm-1,
while the alkaline form exhibited a broad CO-stretching band at 1948 cm-1
with a half-band width of 33 cm-1. Significance of these results are
discussed in relation to the structure of the heme vicinity on the CO
complex of cytochrome c peroxidase.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
