title: Mechanisms of inhibition of phenylalanine ammonia-lyase by phenol inhibitors and phenol/glycine synergistic inhibitors.
abstract: Phenylalanine ammonia-lyase (PAL) catalyzes the beta-elimination of ammonia from L-phenylalanine to trans-cinnamic acid. A study of inhibition of PAL by phenol, ortho-cresol, and meta-cresol gave mixed inhibition; para-cresol is not an inhibitor. The calculated values of K(i) and alphaK(i) are phenol, K(i)=2.1+/-0.5 mM and alphaK(i)=3.45+/-0.95 mM; ortho-cresol, K(i)=0.8+/-0.2 mM and alphaK(i)=3.4+/-0.2 mM; meta-cresol, K(i)=2.85+/-0.15 mM and alphaK(i)=18.5+/-1.5 mM. The synergistic inhibition of the same inhibitors with glycine showed a lack of inhibition with the para-cresol/glycine pair, while mixed inhibition was observed with the ortho-cresol/glycine pair (K(i)=0.038+/-0.008 mM, alphaK(i)=0.13+/-0.04 mM) and phenol/glycine pair (K(i)=0.014+/-0.003 mM, alphaK(i)=0.058+/-0.01 M). The meta-cresol/glycine pair gave competitive inhibition (K(i)=0.36+/-0.076 mM). The strong synergistic inhibition observed implies that the inhibitors bind at the active site: in fact, the inhibitors used imitate the structure of the substrate. The order of synergistic inhibition is the same for the sites related to K(i) and alphaK(i). These results are in agreement with the inhibitors entering two active sites located in two different subunits.
authors.affiliation: Dipartimento di Chimica, Universitá degli Studi di Perugia, 06123 Perugia, Italy. alunnis@unipg.it
authors.forename: Sergio
authors.initials: S
authors.lastname: Alunni
authors.forename: Antonio
authors.initials: A
authors.lastname: Cipiciani
authors.forename: Giovanna
authors.initials: G
authors.lastname: Fioroni
authors.forename: Laura
authors.initials: L
authors.lastname: Ottavi
mesh_terms: D020134:Catalytic Domain; D003408:Cresols / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D005998:Glycine / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D066298:In Vitro Techniques; D007700:Kinetics; D008956:Models, Chemical; D019800:Phenol / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D010636:Phenols / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology*; D010650:Phenylalanine Ammonia-Lyase / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism; D021122:Protein Subunits; D012248:Rhodotorula / Q000201:enzymology
chemical_list: D003408:Cresols; D004791:Enzyme Inhibitors; D010636:Phenols; D021122:Protein Subunits; C032538:4-cresol; D019800:Phenol; D010650:Phenylalanine Ammonia-Lyase; C042041:3-cresol; D005998:Glycine; C034047:2-cresol