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Biosynthesis of δ -aminolevulinic acid from the Intact Carbon Skeleton of Glutamic Acid in Greening Barley
Samuel I. Beale, Simon P. Gough and S. Granick
Proceedings of the National Academy of Sciences of the United States of America
Vol. 72, No. 7 (Jul., 1975), pp. 2719-2723
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/64793
Page Count: 5
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The customary route in animals and bacteria for δ -aminolevulinic acid biosynthesis is from glycine and succinyl CoA, catalyzed by the enzyme δ -aminolevulinic acid synthetase [succinyl-CoA:glycine C-succinyltransferase (decarboxylating), EC 22.214.171.124]. Attempts to demonstrate this route in plants have been unsuccessful. Evidence is given for a new enzymic route of synthesis of δ -aminolevulinic acid in plants. This route involves the incorporation of the intact five-carbon skeleton of glutamic acid into δ -aminolevulinic acid. Demonstration of the new pathway in plants has been made by feeding specifically labeled [14C]glutamic acid to etiolated barley shoots greening in the light. In the presence of levulinate, a competitive inhibitor of δ -aminolevulinic acid dehydratase [porphobilinogen synthase; δ -aminolevulinate hydro-lyase (adding δ -aminolevulinate and cyclizing); EC 126.96.36.199], δ -aminolevulinate accumulates. The δ -aminolevulinate formed was chemically degraded by periodate to formaldehyde and succinic acid. The C5 (formaldehyde) fragment was separated, as the 5,5-dimethyl-1,3-cyclohexanedione (dimedone) derivative, from the C1-C4 (succinic acid) fragment. The C5 atom contained radioactivity predominantly derived from C1 of glutamic acid. Conversely, the labeled C3 and C4 atoms of glutamic acid were found primarily in the succinic acid (C1-C4) fragment of δ -aminolevulinate. This labeling pattern for δ -aminolevulinic acid is consistent with a biosynthetic route utilizing the intact five-carbon skeleton of α -ketoglutarate, glutamate, or glutamine, and is inconsistent with the δ -aminolevulinic acid synthetase pathway utilizing glycine and succinyl CoA as precursors.
Proceedings of the National Academy of Sciences of the United States of America © 1975 National Academy of Sciences