-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.

See also: Porphyrin and Heme Metabolism

INTERNET LINKS:

> 1. Porphyrin and Chlorophyll Metabolism

> 2. Photosynthetic Pigments