Biology Reference
In-Depth Information
Chapter 5
Reactions Between
δ
-Aminolevulinic
Acid and Protoporphyrin IX
A solid edifice has to be built on solid foundations
(Constantin A. Rebeiz).
The reactions between ALA and Proto are shared between heme and Chl biosynthesis.
Since most of the Chl biosynthetic heterogeneity is rooted in reactions further down
the Chl biosynthetic pathway, the reactions between ALA and Proto will be briefly
discussed.
All tetrapyrroles that will be discussed in this review are derivatives either of
Porphin or Phorbin (Fig.
5.1
). Because of its simplicity, the Fischer nomenclature
and numbering systems will be used throughout this overview. The sequence of
reactions between
-aminolevulinic acid (ALA) and protoporphyrin IX (Proto) are
depicted in Fig.
5.2
.
In higher plant thylakoids, the reactions between ALA and Proto are considered to
take place in five different environments and may involve both spatial and chemical
biosynthetic heterogeneities. Chlorophyll biosynthetic heterogeneity (see Synopsis
biosynthetic heterogeneity, or (c) to a combination of spatial and chemical biosyn-
thetic heterogeneities (Rebeiz et al.
2003
). Spatial biosynthetic heterogeneity refers to
the biosynthesis of an anabolic tetrapyrrole or end product by identical sets of
enzymes, at several different locations of the thylakoid membranes. On the other
hand, chemical biosynthetic heterogeneity refers to the biosynthesis of an anabolic
tetrapyrrole or end product at several different locations of the thylakoid membranes,
via different biosynthetic routes, each involving at least one different enzyme. This
hypothesis is based on the detection of resonance excitation energy transfer from
Proto to various Chl-protein complexes in multiple thylakoid environments
(Table
5.1
). It is also based on the observed resonance excitation energy transfer
from Proto to Pchlide
a
. In addition, Averina and coworkers have proposed the
existence of at least two types of Chl biosynthesis centers which differ in their ability
of form ALA (Averina et al.
1993
;Averina
1998
).
δ
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