Journal
GENE
Volume 427, Issue 1-2, Pages 86-92Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.gene.2008.09.005
Keywords
phylogenetic tree; genome duplications; positive cooperativity; allosterism; phenylalanine catabolism
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The social amoeba Dictyostelium discoideum contains only one aromatic amino acid hydroxylase (AAAH) gene compared to at least three in metazoans. As shown in this work this gene codes for a phenylalanine hydroxylase (DictyoPAH) and phylogenetic analysis places this enzyme close to the precursor AAAHs, aiding to define the evolutionary history of the AAAH family. DictyoPAH shows significant similarities to other eukaryote PAH, but it exhibits higher activity with tetrahydrodictyopterin (DH4) than with tetrahydrobiopterin (BH4) as cofactor. DH4 is an abundant tetrahydropterin in D. discoideum while BH4 is the natural cofactor of the AAAHs in mammals. Moreover, DictyoPAH is devoid of the characteristic regulatory mechanisms of mammalian PAH such as positive cooperativity for L-Phe and activation by preincubation with the substrate. Analysis of the few active site substitutions between DictyoPAH and mammalian PAR including mutant expression analysis, reveals potential structural determinants for allosteric regulation. (C) 2008 Elsevier B.V. All rights reserved.
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