Reactions Between b-Aminolevulinic Acid and Protoporphyrin IX - Chlorophyll Biosynthesis and Technological Applications - page 169

5.1 Biosynthetic Heterogeneity of Delta-Aminolevulinic
Acid (ALA)

δ -Aminolevulinic acid (5-aminolevulinic acid) is the building block of all

tetrapyrroles in nature. It is synthesized via a different pathway in animal cells
and lower plants than in green plants (Fig. 5.3 ).

5.1.1 Biosynthesis of ALA in Animal Cells

In animal cells, ALA is formed by condensation of glycine and succinyl-CoA
(Gibson et al. 1958 ). The reaction is catalyzed by ALA synthetase and takes
place in the mitochondria. The biosynthesis of succinyl-CoA from succinic acid
is catalyzed by succinyl-thiokinase in the presence of Mg ++ and ATP, and takes
place as well in the mitochondria. ALA is exported to the cytoplasm for further
metabolism (Granick 1963 ). In animal mitochondria ALA is mainly destined for the
biosynthesis of Proto and heme (Rebeiz et al. 1996 ) (Fig. 5.4 ).

5.1.2 Biosynthesis of ALA in Lower Plants

In Rhodopseudomonas spheroides , a bacterium (Chen et al. 1981 ), Scenedesmus
obliquus (Klein and Senger 1978 ) unicellular green alga, and in Euglena gracilus
(Beale et al. 1981 ) a unicellular green flagellate alga, two pathways using, either
glycine and succinyl-CoA (see above), or incorporating the whole C-5-skeleton
of glutamate into ALA (see below) are functional in the biosynthesis of ALA.
In Scenedesmus both pathways appear to contribute to Chl formation in the light.
In Euglena , it was proposed that ALA synthesis via glycine and succinyl-CoA is
responsible for non-plastid tetrapyrrole biosynthesis (Beale et al. 1981 ). These
results stress the need to investigate in more depth the molecular basis and
biological significance of the ALA biosynthetic heterogeneity in a wider range of
lower and higher plants.

Fig. 5.3 δ -Aminolevulinic
acid (ALA)

Fig. 5.4 (a) Glycine and
(b) succinate molecules