title: Amine cations promote concurrent conversion of prohistidine decarboxylase from Lactobacillus 30a to active enzyme and a modified proenzyme.
abstract: Activation of prohistidine decarboxylase (pi 6) from Lactobacillus 30a proceeds by an intramolecular, pH- and monovalent cation-dependent reaction in which its constituent pi chains are cleaved nonhydrolytically between Ser-81 and Ser-82 with loss of NH3 and conversion of Ser-82 to the pyruvoyl residue of active histidine decarboxylase (alpha beta)6. Amines with pKa values more than 7.0 substitute for K+ or NH4+ in the activation of prohistidine decarboxylase, but they also catalyze its inactivation in a competing reaction, pi 6----pi'6. Sequence analysis of the appropriate tryptic peptide from amine-inactivated prohistidine decarboxylase established that inactivation results from conversion of Ser-82 of the pi chain to an aminoacrylate residue. The inactivated proenzyme (pi'6) does not form histidine decarboxylase; this fact eliminates one of two postulated mechanisms of activation and, thus, favors activation by beta-elimination of the acyl group of an intermediate ester formed between Ser-81 and Ser-82. L-Histidine is bound by the proenzyme (Kd = 1.7 x 10(-4) M) and is an effective activator; one binding site is present per pi subunit. K+, NH4+, and Na+ competitively inhibit (Ki values = 2.8-4.4 x 10(-3) M) activation by histidine. The data suggest the presence of two classes of monovalent cation binding sites on prohistidine decarboxylase: one (near Ser-82) is readily saturable and one is unsaturable even by 2.4 M K+.
authors.affiliation: Department of Chemistry, University of Texas, Austin 78712.
authors.forename: P D
authors.initials: PD
authors.lastname: van Poelje
authors.forename: E E
authors.initials: EE
authors.lastname: Snell
mesh_terms: D000588:Amines / Q000494:pharmacology*; D002262:Carboxy-Lyases / Q000235:genetics*; D002414:Cations, Monovalent; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism*; D006640:Histidine Decarboxylase / Q000235:genetics*; D007700:Kinetics; D007778:Lactobacillus / Q000201:enzymology*; D011499:Protein Processing, Post-Translational / Q000187:drug effects
chemical_list: D000588:Amines; D002414:Cations, Monovalent; D004792:Enzyme Precursors; D002262:Carboxy-Lyases; D006640:Histidine Decarboxylase