Biology Reference
In-Depth Information
16.5 What Kind of Scientific Knowledge Is Needed
to Bioengineer a Reduction in PSU Size
Thorough and integrated anabolic and catabolic knowledge in the following fields
of research is needed for successful research aimed at the bioengineering of a
reduced PSU size. That include:
(a) Chls,
(b) lipids,
(c) carotenoids,
(d) plastoquinones,
(e) chloroplast apoproteins,
(f) assembly of pigment-protein complexes.
Because of space limitations, the remainder of this discussion will focus on the
Chl, and apoprotein components of chloroplasts as well as on the assembly of
Chl-protein complexes.
16.5.1 State of the Art in Our Understanding
of Chl Biosynthesis
During the past 30 years, it has become apparent that contrary to previous beliefs,
the Chl biosynthetic pathway, is not a simple single-branched pathway, but a
complex multibranched pathway that consist of about 15 carboxylic and two fully
multibranched carboxylic pathways are briefly discussed below. Because of the
importance of Chl-apoprotein assembly for the bioengineering of smaller photo-
synthetic units, these topics will also be discussed in this chapter which will create
16.5.1.1 The Single-Branched Chl Biosynthetic Pathway Does Not
Account for the Formation of All the Chl in Green Plants
The single-branched Chl biosynthetic pathway is depicted below in Fig.
16.2
.
It consists of a linear sequence of biochemical reactions which convert divinyl
(DV) protoporphyrin IX (Proto) to monovinyl (MV) Chl
a
via DV Mg-Proto, DV
Mg-Proto monomethyl ester (Mpe), DV protochlorophyllide
a
(Pchlide
a
), MV
Pchlide
a
, and MV Chlorophyllide
a
(Chlide
a
). The salient features of this pathway
are (a) the assumption that DV Pchlide
a
does not accumulate in higher plants, but
is a transient metabolite which is rapidly converted to MV Chl
a
via MV Pchlide
a
,
and (b) that the formation and accumulation of MV tetrapyrroles between Proto
and Mpe and DV tetrapyrroles between Pchlide
a
and Chl
a
does not take place
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