title: Regulation of the aromatic pathway in the cyanobacterium Synechococcus sp. strain Pcc6301 (Anacystis nidulans).
abstract: A pattern of allosteric control for aromatic biosynthesis in cyanobacteria relies upon early-pathway regulation as the major control point for the entire branched pathway. In Synechococcus sp. strain PCC6301 (Anacystis nidulans), two enzymes which form precursors for L-phenylalanine biosynthesis are subject to control by feedback inhibition. 3-Deoxy-D-arabino-heptulosonate 7-phosphate synthase (first pathway enzyme) is feedback inhibited by L-tyrosine, whereas prephenate dehydratase (enzyme step 9) is feedback inhibited by L-phenylalanine and allosterically activated by L-tyrosine. Mutants lacking feedback inhibition of prephenate dehydratase excreted relatively modest quantities of L-phenylalanine. In contrast, mutants deregulated in allosteric control of 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase excreted large quantities of L-phenylalanine (in addition to even greater quantities of L-tyrosine). Clearly, in the latter mutants, the elevated levels of prephenate must overwhelm the inhibition of prephenate dehydratase by L-phenylalanine, an effect assisted by increased intracellular L-tyrosine, an allosteric activator. The results show that early-pathway flow regulated in vivo by 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase is the dominating influence upon metabolite flow-through to L-phenylalanine. L-Tyrosine biosynthesis exemplifies such early-pathway control even more simply, since 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase is the sole regulatory enzyme subject to end-product control by L-tyrosine.
mesh_terms: D010723:3-Deoxy-7-Phosphoheptulonate Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000446:Aldehyde-Lyases / Q000378:metabolism*; D000458:Cyanobacteria / Q000201:enzymology* / Q000235:genetics; D004789:Enzyme Activation; D005809:Genes, Regulator; D006836:Hydro-Lyases / Q000378:metabolism*; D009154:Mutation; D010649:Phenylalanine / Q000096:biosynthesis* / Q000494:pharmacology; D011302:Prephenate Dehydratase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014443:Tyrosine / Q000494:pharmacology
chemical_list: D014443:Tyrosine; D010649:Phenylalanine; D010723:3-Deoxy-7-Phosphoheptulonate Synthase; D000446:Aldehyde-Lyases; D006836:Hydro-Lyases; D011302:Prephenate Dehydratase