l-Phenylalanine Ammonia-Lyase (Maize): Evidence for a Common Catalytic Site for l-Phenylalanine and l-Tyrosine.

摘要: l-Phenylalanine ammonia-lyase (E.C. 4.3.1.5) from maize is active with l-tyrosine and l-phenylalanine exhibits atypical Michaelis-Menten kinetics both substrates. With phenylalanine as a substrate, the pH optimum 8.7 tyrosine, 7.7. The estimated Km at high substrate concentrations 0.27 mm for 0.029 tyrosine. However, V(max) eight times higher than tyrosine when are measured 8.7, 7 their optima. following evidence leads us to conclusion that there common catalytic site substrates: (a) It impossible appreciably alter ratio of two activities during purification isoelectric focusing. (b) products formed in mixed experiments good agreement predicted values. (c) NaBH(4) reduces same degree l-phenylalanine, l-tyrosine, cinnamate, p-coumarate protect against reduction degree. In contrast, enzyme isolated potato, which does not act on protected by either or p-coumarate. enzymes appear have dehydroalanine-containing prosthetic group.