Plant Physiology 62:10-13 (1978)
© 1978 American Society of Plant Biologists
Articles
Two Biosynthetic Pathways to  -Aminolevulinic Acid in a Pigment Mutant of the Green Alga, Scenedesmus obliquus 1
Otto Klein and
Horst Senger
Botanisches Institut, University of Marburg, Marburg, Germany
Pigment mutant C-2A' of the unicellular green alga Scenedesmus obliquus develops only traces of chlorophyll and has no detectable amount of  -aminolevulinic acid (ALA) when grown in the dark. In light it develops ALA and in the presence of levulinic acid (LA), a competitive inhibitor of ALA dehydratase, it accumulates 0.18 mmoles of ALA per 10 microliters of packed cell volume per 12 hours. This amount could be increased up to 15 times by feeding precursors and cofactors.
Incubation with [U-14C]glutamate, [1-14C]glutamate, and [2-14C]glycine yielded significantly labeled ALA, whereas [1-14C]glycine did not label the ALA specifically. Thus, two pathways using either glycine/succinyl-coenzyme A or incorporating the whole C-5-skeleton of glutamate into ALA are present in this alga. The efficiency of the glycine/succinyl-coenzyme A pathway seems to be three times higher than that of the glutamate pathway. Incubation with [5-14C]2-ketoglutarate, which can serve both pathways as a precursor, resulted in radioactivity of ALA as high as the sum of both labeling with [1-14C]glutamate and [2-14C]glycine.
Since the newly synthesized chlorophyll was radioactive regardless of labeled substrate employed, both pathways culminate in chlorophyll formation.
1 Supported by the Deutsche Forschungsgemeinschaft. The results of the current publication have partially been presented at the Annual European Symposium on Photomorphogenesis 1977, March 19-25, Rehovot, Israel.
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