Biology Reference
In-Depth Information
Fig. 9.8 Spectral Shifts of the Ternary Pchlide
a
-NADPH-Apoprotein Complex During the
Photoconversion of Pchlide
a
to Chl(ide)
a
.“E” and “F” refer to the red fluorescence excitation
and emission maxima respectively at 77 K
9.5.3 Spectral Shift III
Shift III, which converts Chlide
a
(E676 F690) to Chlide
a
(E682 F697) takes place
very rapidly in darkness. It was considered by Sironval et al. (
1967
) to lead to the
formation of a mature Chlide
a
-apoprotein complex that releases Chlide
a
from
the Pchlide a oxidoreductase complex. This in turn allows PORA to pick up another
Pchlide
a
chromophore to yield t-LW-Pchlide
a
-H (E650 F655).
9.5.4 Spectral Shift IV
The conversion of Chlide
a
(E682 F697) to Chl(ide)
a
(E672 F680) species was the
first spectral shift to be described during the conversion of Pchlide
a
to Chl(ide)
a
.
It was reported by
Shibata in 1957
,
as a spectral shift that took place in darkness or
in the light in about 10-20 min after the onset of illumination, depending on the age
of the etiolated tissue, and the plant species. During this shift Chlide
a
is esterified
with geranylgeraniol, which is reduced stepwise to phytol (
see section dealing with
9.5.5 Spectral Shift V
The fifth shift was also described by Shibata (
1957
). It takes place either in the light
or in darkness, and corresponds to the final integration of Chl
a
into various pigment
proteins of the thylakoid membranes. On the basis of energy transfer from Pchlide
a
(E650 F655) to Chlide
a
(E682 F697) at fractional or partial photoconversions,
Thorne (
1971
) concluded that diffusion of the chromophore from the apoprotein
occurs at the level of Chl(ide)
a
(E674 F683) (shift V) instead of Chlide
a
(E682
F697) as proposed by Sironval et al. (
1967
). From the maximal appearance of the
(E668 F6740) photointermediate and the Pchlide
a
and Chlide
a
content Thorne
(
1971
) proposed that the Pchlide
a
aggregate comprised about 20 molecules of
Pchlide
a
.
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