Biology Reference
In-Depth Information
Chapter 12
The Chlorophyll
b
Biosynthetic Pathway:
Novel Metabolic Intermediates
Imagination is more important than knowledge (Albert
Einstein).
12.1 Prologue
The demonstration of metabolic pathways is a multistep process. It involves at least
three stages: (a) the detection and characterization of metabolic intermediates, (b) the
demonstration of precursor-product relationships between putative intermediates, and
(c) purification and characterization of enzymes involved in the metabolic intercon-
versions. These criteria will be applied in our evaluation of the experimental evidence
that supports the operation of a multibranched Chl
b
biosynthetic pathway in green
(ing) plants.
During the past two decades, several putative metabolic intermediates of the Chl
b
biosynthetic pathway have been detected in higher and lower plants. These
intermediates are discussed below.
12.2 Monovinyl Protochlorophyllide
b
(MV Pchlide
b
)
The discovery of protochlorophyllide (Pchlide)
b
in higher plants was reported by
Shedbalkar et al. (
1991
). It was first observed as a fluorescent compound at 77 K in
diethyl ether, with Soret excitation and red emission maxima at 463 and 643 nm
respectively. These fluorescence properties were identical to those of synthetic
Pchlide phytyl ester
b
. The chemical structure of the latter was confirmed by proton
nuclear magnetic resonance, fast atom bombardment mass spectroscopic analysis
and chemical derivatization coupled to electronic spectroscopic analysis
(Shedbalkar et al.
1991
). MV Pchlide
b
differed fromMV Pchlide
a
by the presence
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