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In bacteria, biosynthesis of coenzyme A is well established. In Escherichia coli, Aspartate is decarboxylated to form β-alanine. Hydroxymethylation of α-ketoisovalerate by tetrahydrofolate-dependent hydrooxymethyltransferase followed by NADPH dependent reduction synthesizes panthoic acid. β-alanine and panthoic acid are condensed in the presence of ATP-Mg to give pantothenic acid. This is proceeded by pantothenate kinase mediated phosphorylation, condensation with cysteine and then decarboxylation to give phosphopantetheine. Coenzyme A is then formed by adenylation and phosphorylation of phosphopantetheine. The pathway is regulated by coenzyme A and its thioesters feedback inhibition of phosphorylation (panthothenate kinase) of pantothenic acid. In yeast (Saccharomyces cerevisiae), pantothenic acid is rather first adenylated, condensed with cysteine, and decarboxylated followed by phosphorylation to synthesize coenzyme A (Begley et al., 2001). Unlike bacteria, yeast and plants, animals depend for pantothenic acid on their diet (Genschel, et al., 1999).
Recent research on Coenzyme A biosynthesis in plantsinclude partial purification of pantothenate kinase (Falk and Guerra, 1993), and oxopanthyol lactone reductase from spinach (Spinacia oleracea) (Julliard, 1994), characterization and cloning of panthothenate synthetase from Lotus japonica and rice (Oryza sativum) (Genschel, et al., 1999) and two Arabidopsis genes (AtHal3a and AtHal3b) whose proteins have less than 20% homology to flavin coenzymes from E. coli, putatively involved in pantothenate synthesis (Esponosa-Ruiz et al., 1999).
Related Articles:
Coenzyme A.
Biosynthesis of Coenzyme A in plants. |
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Last Updated on Monday, 12 October 2009 |
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