Biology Reference
In-Depth Information
Chapter 11
The Fully Esterified Chlorophyll
a Biosynthetic Routes: Reactions Between
Mg-Protoporphyrin IX Diester and Chl a
It takes excellence to recognize excellence, while mediocrity
breeds mediocrity.
11.1 The Mg-Proto Diester Pool
The Mg-proto diester (Mpde) pool (Fig.
11.1
) consists of the first metabolic
intermediates of the fully esterified Chl
a
biosynthetic route (Fig.
11.2
).
The fully esterified Chl
a
pathway is populated by tetrapyrroles with a methyl
propionate residue at position 6 of the macrocycle and a propionic acid residue at
position 7 which is esterified with one of several different long chain fatty alcohols
(LCFAs) (Rebeiz et al.
2003
) (Fig.
11.1
). The two sets of reactions depicted in
Fig.
11.2
, deal with the least understood phases of the intermediary metabolism of
Chl
a
. In our opinion, the unjustified neglect of this facet of Chl
a
biosynthesis is
caused by several factors, among which (a) occurrence of the metabolic intermediates,
often in very small amounts, (b) slow reaction rates, (c) analytical difficulties,
and (d) early misconceptions that ruled out the role of Pchlide ester as a metabolic
intermediate in Chl biosynthesis (Rebeiz et al.
2003
).
11.1.1 Heterogeneity of the Mg-Proto Diester Pool
A fully esterified Mpde pool was first detected in etiolated cucumber cotyledons
incubated overnight with ALA and Dpy in darkness (McCarthy et al.
1981
). The
novel pool exhibited the chromatographic properties of a fully esterified metallopo-
rphyrin and the spectrofluorometric properties of Mg-Proto. Chemical derivatiza-
tion coupled to spectrofluorometric and chromatographic analysis identified it as
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