Delta-aminolevulinic acid (ALA) is the obligatory precursor for the synthesis
of all tetrapyrroles including porphyrin derivatives such as chlorophyll and
heme. ALA can be synthesized via two different pathways: the Shemin (or C4)
pathway which involves the single step condensation of succinyl-CoA and
glycine and which is catalyzed by ALA synthase (EC 2.3.1.37) and via the C5
pathway from the five-carbon skeleton of glutamate. The C5 pathway operates
in the chloroplast of plants and algae, in cyanobacteria, in some eubacteria
and in archaebacteria.
The initial step in the C5 pathway is carried out by glutamyl-tRNA reductase
(GluTR) [1] which catalyzes the NADP-dependent conversion of glutamate-tRNA(Glu) to glutamate-1-semialdehyde (GSA) with the concomitant release of
tRNA(Glu) which can then be recharged with glutamate by glutamyl-tRNA
synthetase.
GluTR is a protein of about 50 Kd (467 to 550 residues) which contains a few
conserved region. The best conserved region is located in positions 99 to 122
in the sequence of known GluTR. This region seems important for the activity
of the enzyme. We have developed a signature pattern from that conserved
region.
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