Phenylalanine ammonia-lyase: enzymic conversion of 3-(1,4-cyclohexadienyl)-L-alanine to trans-3-(1,4-cyclohexadienyl)acrylic acid

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Abstract
The phenylalanine analog 3-(1,4-cyclohexadienyl)-L-alanine is converted to the hitherto unknown cinnamate analog trans-3-(1,4-cyclohexadienyl)acrylic acid by L-phenylalanine ammonia-lyase (EC 4.3.1.5) from maize, potato or Rhodotorula glutinis. The structure assigned to the product is confirmed by its 1H NMR spectrum and by the chemical synthesis to be described in a subsequent paper. On comparing the above substrate analog with L-phenylalanine, the Km was lowered only slightly but kcat was reduced 14- to 40-fold depending on the source of the enzyme. Because the compounds closely resemble each other in size and hydrophobic properties, this lowering of kcat may be due to the electronic effect of replacing the .pi. electrons of the aromatic system by those of a double bond. Correct alignment at the active site depends on the space-filling properties of the ring system; open chain analogs that retain the .gamma.,.delta. double bond were inhibitors, not substrates.
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