Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Plant Physiology 72:1056-1061 (1983)
© 1983 American Society of Plant Biologists

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Alternative Routes for the Synthesis of 5-Aminolevulinic Acid in Maize Leaves 1

I. Formation from 2-Ketoglutarate via 4,5-Dioxovaleric Acid

Eitan Harel2, Emma Ne'Eman and Erna Meller

Department of Botany, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

Cell-free extracts from greening maize (Zea mays L.) leaves catalyze the conversion of [14C]2-ketoglutarate (KG) to [14C]5-aminolevulinic acid (ALA) in a reaction which requires NADH and an amino donor and shows maximal activity around pH 6.5. The enzymic system is located in the cytosol. This cell fraction contains a low level of `KG dehydrogenase' activity and a transaminase which catalyzes the conversion of 4,5-dioxovaleric acid (DOVA) to ALA. The transaminase can use glutamate, aspartate, or alanine as amino donor. It is effectively inhibited by aminooxyacetate and ethylenediamine tetraacetate and shows maximal activity at pH 6.7. The activity of DOVA transaminase is only slightly affected by preillumination of leaves and can also be detected in green leaves and in roots.

DOVA was isolated from leaves and roots and determined as its benzoquinoxaline derivative. Significant amounts were found only in tissues in which ALA had accumulated or after it was exogenously supplied. DOVA was labeled in vivo by both [14C]ALA and [14C]KG. Small amounts were also formed from ALA in a cell-free system.

It is suggested that DOVA may be an intermediate in the diversion of ALA to respiratory metabolism and that it is not involved in the biosynthesis of this porphyrin precursor.

2 To whom correspondence should be addressed.

1 Supported by grant No. 866 from the United States-Israel Binational Science Foundation and a grant from The Israel Academy of Sciences and Humanities—Basic Research Foundation.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1983 by the American Society of Plant Biologists