The Fully Esterified Chlorophyll a Biosynthetic Routes: Reactions Between Mg-Protoporphyrin IX Diester and Chl a - Chlorophyll Biosynthesis and Technological Applications - page 264

Fig. 11.3 DV Mg-Proto
diester (DV Mpde)
Mg-Proto diester (Mpde). Mpde was also detected in dark-grown Euglena gracilis
and in etiolated cucumber cotyledons incubated in darkness with ALA, in the
presence and absence of added Dpy. Upon detection of Mpde, it was suggested to
be a metabolic precursor of the fully esterified, heterogeneous, Pchlide a ester pool
(Belanger and Rebeiz 1982 ; McCarthy et al. 1981 ).
The Mpde pool exhibits a well pronounced DV-MV chemical heterogeneity
(Belanger and Rebeiz 1982 ). For example in etiolated cucumber cotyledons
incubated in darkness with ALA and Dpy, as well as in dark-grown Euglena gracilis,
the Mpde pool consisted of DV and MV Mpde components. In general the propor-
tion of DV Mpde was higher than that of MV Mpde, except in Euglena .
High-pressure liquid chromatographic analysis has also indicated that the Mpde
pool was heterogeneous at position 7 of the macrocycle and consisted of three fully
esterified Mg-Protos. Gas-chromatographic /mass spectroscopic analysis of the
saponified alcohol fraction of the heterogeneous Mpde pool revealed that the latter
consisted of three major long-chain alcohols, none of which was identifiable with
known isoprenoids such as, farnesol or phytol (McCarthy et al. 1981 ). In addition to
the heterogeneity of the long chain alcohols esterifying the propionic acid residue at
position 7 of the macrocycle, the Mpde pool exhibited a well pronounced DV-MV
chemical heterogeneity (see above) (Belanger and Rebeiz 1982 ).
11.1.1.1 The Divinyl Mpde Pool
Divinyl Mg-Proto diester (Mpde) has two vinyl groups at positions 2 and 4 of the
tetrapyrrole macrocycle (Fig. 11.3 ). The DV nature of the DV component of the Mpde
pool of higher plants was determined by chemical derivatization coupled to analytical
fluorescence spectroscopy at 77 K (Belanger and Rebeiz 1982 ).
The biosynthetic origin of DV Mpde is not presently clear, and is tentatively
assigned toDVMpe esterification (Fig. 11.2 , route 17). After its detection in cucumber
cotyledons and in Euglena cultures (Belanger and Rebeiz 1982 ), DV Mpde, has
been proposed as a precursor of fully esterified DV Pchlide a , i.e. DV Pchlide
a ester (DV Pchlide a E) (Fig. 11.2 , Route 17). A precursor-product relationship
between DV Mpde and DV Pchlide a E remains to be established and is complicated
by the presence of Mpde esterases that convert exogenous Mpde to Mpe (Rebeiz,
unpublished).