-Aminolevulinic Acid (ALA)

-Aminolevulinic acid (ALA) is a common intermediate in the biosynthetic pathways of heme, chlorophylls, phycobilins, and cobalamins. Relationships between the various pathways are shown in Figure 21.27.

In animals, all of the nitrogens of heme are derived from glycine and all of the carbons are derived from succinate and glycine. The pathway is also called the succinate-glycine pathway. The first step in the process is catalyzed by a pyridoxal phosphate-containing enzyme, -aminolevulinic acid synthetase (ALA synthestase) (Figure 21.28).

In plants, ALA is made in a process that begins with glutamate, which becomes linked to a tRNA (Figure 21.29). In plants, synthesis of ALA is regulated by light.

1. Porphyrin and Chlorophyll Metabolism

2. Photosynthetic Pigments