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about 95 % Pchlide
a
and about 5 % Pchlide
a
ester (Pchlide a E). The latter is
esterified with long chain fatty alcohols (LCFAs) at position 7 of the macrocycle.
While Pchlide a E consists mainly of MV Pchlide
a
ester, Pchlide
a
consists of DV
and MV Pchlide
a
. The latter are the immediate precursors of DV and MV
chlorophyllide (Chlide)
a
. Accumulation of the various tetrapyrrole donors was
induced by incubation of green tissues with delta-aminolevulinic acid (ALA) and/or
2,2
0
-dipyridyl (Rebeiz et al.
1988
).
The task of selecting appropriate Chl a-protein acceptors was facilitated by the
fluorescence properties of green plastids. At 77
K, emission spectra of isolated
chloroplasts exhibit maxima at 683-686 nm (~F685), 693-696 nm (~F695), and
735-740 nm (~F735). It is believed that the fluorescence emitted at ~ F685 nm
arises from the Chl
a
of LHCII, the major thylakoid LHC antenna, and LHCI-680,
one of the LHC antennae of PSI (Bassi et al.
1990
). That emitted at ~F695 nm is
believed to originate mainly from the Chl
a
of CP47 and CP29, two PSII antennae
(Bassi et al.
1990
). That emitted at ~F735 nm is believed to originate primarily from
the Chl
a
of LHCI-730, a PSI antenna (Bassi et al.
1990
). Since these emission
maxima are readily observed in the fluorescence emission spectra of green tissues
and are associated with definite thylakoid Chl
a
-protein complexes, it was
conjectured that they would constitute a meaningful resource for monitoring exci-
tation resonance energy transfer between anabolic tetrapyrroles and representative
Chl
a
-protein complexes. To monitor the possible occurrence of resonance energy
transfer between the accumulated anabolic tetrapyrroles and Chl
a
-protein
complexes, excitation spectra were recorded at 77
K at the respective emission
maxima of the selected Chl
a
acceptors, namely at ~685, ~695, and ~735 nm. It was
conjectured that if resonance energy transfers were to be observed between the
tetrapyrrole donors and the selected Chl a acceptors, definite excitation maxima
would be observed. These excitation maxima would correspond to absorbance
maxima of the various tetrapyrrole donors, and would represent the peaks of the
excitation resonance energy transfer bands (Kolossov et al.
2003
).
Pronounced excitation resonance energy transfer bands from Proto, Mp(e), and
Pchl(ide)
a
to Chl
a
~F685, ~F695, and ~F735 were detected as shown in Table
6.1
,
which is depicted below.
It was proposed that the various intra-membrane environment of Proto, Mp
(e) and Pchl(ide) which were manifested by a differential donation of excitation
resonance energy transfer to different Chl
a
-apoprotein complexes represent evi-
dence of Chl spatial biosynthetic heterogeneity (Kolossov et al.
2003
)
6.2.2 Why Is Tetrapyrrole Metabolism Important
Heme and chlorophyll (Chl) are porphyrins. Porphyrins (also referred to as
tetrapyrroles) are essential for life in the biosphere). Chlorophyll catalyzes the
conversion of solar energy to chemical energy via the process of photosynthesis.
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