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Fig. 11.4 The MV
Mg-Proto diester pool
(MV MpeE)
11.1.1.2 The MV Mpde Pool
Monovinyl Mg-Proto diester (MV Mpde) has one vinyl groups at positions
2 and one ethyl group at position 4 of the tetrapyrrole macrocycle (Fig.
11.4
).
The MV nature of the Mpde pool of higher plants was determined by chemical
derivatization coupled to analytical fluorescence spectroscopy at 77 K (Belanger
and Rebeiz
1982
) (Fig.
11.4
).
The biosynthetic origin of MV Mpde is not presently clear, and is tentatively
assigned to MV Mpe esterification (Fig.
11.2
, route 16). After its detection in
cucumber cotyledons and in
Euglena
cultures where it is the main constituent of
the Mpde pool (Belanger and Rebeiz
1982
), MV Mpde has been proposed as a
precursor of MV Pchlide
a
E (Fig.
11.2
, route 16). A precursor-product relationship
between MV Mpde and DV Pchlide
a
E remains to be established and is compli-
cated by the presence of Mpde esterases that convert exogenous Mpde to Mpe
(Rebeiz, unpublished).
11.1.2 Pchlide a Ester
Pchlide
a
E is one of the least understood pools of the Chl biosynthetic pathway and
its history is steeped in controversy (Fig.
11.5
). Fischer and Oestreicher (
1940
)
synthesized the phytyl ester of Pchlide
a
and showed that it differed from MV Chl
a
by having two fewer hydrogens at position 7 and 8 of the macrocycle. They
named this molecule protochlorophyll. Because of the structural similarity between
Pchlide
a
phytyl ester and Chl
a
, the erroneous notion evolved that Pchlide
a
phytyl
ester was the major immediate photoprecursor of Chl
a
(Smith
1948
). When
Granick isolated and identified Pchlide
a
from an X-ray
Chlorella
mutant inhibited
in its capability to form Chl, he considered it to be the immediate precursor of
Pchlide
a
ester. The biological function of Pchlide
a
as the immediate precursor of
chlorophyllide (Chlide)
a
was not fully understood till 7 years later (Wolff and
Price
1957
).
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