BIOSYNTHETIC PATHWAYS TO 6‐AMINOLEVULINIC ACID INDUCED BY BLUE LIGHT IN THE PIGMENT MUTANT C‐2A‘ OF SCENEDESMUS OBLIQUUS*

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Abstract
The X‐ray induced mutant C‐2A of Scenedesmus obliquus grows heterotrophically but forms only traces of chlorophyll in the dark. Upon illumination, baminolevulinic acid (ALA) is synthesized and chlorophyll is formed. These processes are blue light dependent and cease immediately when the cells are transferred back into darkness.Addition of levulinic acid (LA) inhibits the light‐dependent formation of chlorophyll and causes accumulation of ALA by competitive inhibition of the ALA dehydratase (EC. 4.2.1.24). By feeding specifically labelled 14C precursors to the pigment mutant, inhibiting the ALA dehydratase with LA, accumulating, extracting and analyzing the ALA, two pathways leading towards ALA could be established: glycine and succinyl CoA can be condensed to ALA and the 5 carbon skeleton of glutamate can completely be incorporated into ALA via a second pathway.The glycine‐succinyl CoA pathway dominates over the glutamate pathway, but both lead to chlorophyll formation.