title: Inhibition of Escherichia coli porphobilinogen synthase using analogs of postulated intermediates.
abstract: BACKGROUND
  Porphobilinogen synthase is the second enzyme involved in the biosynthesis of natural tetrapyrrolic compounds, and condenses two molecules of 5-aminolevulinic acid (ALA) through a nonsymmetrical pathway to form porphobilinogen. Each substrate is recognized individually at two different active site positions to be regioselectively introduced into the product. According to pulse-labeling experiments, the substrate forming the propionic acid sidechain of porphobilinogen is recognized first. Two different mechanisms for the first bond-forming step between the two substrates have been proposed. The first involves carbon-carbon bond formation (an aldol-type reaction) and the second carbon-nitrogen bond formation, leading to an iminium ion.
  
  
  RESULTS
  With the help of kinetic studies, we determined the Michaelis constants for each substrate recognition site. These results explain the Michaelis-Menten behavior of substrate analog inhibitors - they act as competitive inhibitors. Under standard conditions, however, another set of inhibitors demonstrates uncompetitive, mixed, pure irreversible, slow-binding or even quasi-irreversible inhibition behavior.
  
  
  CONCLUSIONS
  Analysis of the different classes of inhibition behavior allowed us to make a correlation between the type of inhibition and a specific site of interaction. Analyzing the inhibition behavior of analogs of postulated intermediates strongly suggests that carbon-nitrogen bond formation occurs first.
authors.affiliation: Institute of Chemistry, University of Neuchâtel, Neuchâtel, CH-2000, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Jarret
authors.forename: F
authors.initials: F
authors.lastname: Stauffer
authors.forename: M E
authors.initials: ME
authors.lastname: Henz
authors.forename: M
authors.initials: M
authors.lastname: Marty
authors.forename: R M
authors.initials: RM
authors.lastname: Lüönd
authors.forename: J
authors.initials: J
authors.lastname: Bobálová
authors.forename: P
authors.initials: P
authors.lastname: Schürmann
authors.forename: R
authors.initials: R
authors.lastname: Neier
mesh_terms: D000622:Aminolevulinic Acid / Q000737:chemistry / Q000378:metabolism; D001667:Binding, Competitive; D020134:Catalytic Domain; D003998:Dicarboxylic Acids / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics; D008956:Models, Chemical; D011162:Porphobilinogen / Q000737:chemistry / Q000378:metabolism; D000623:Porphobilinogen Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D003998:Dicarboxylic Acids; D004791:Enzyme Inhibitors; D011162:Porphobilinogen; D000622:Aminolevulinic Acid; D000623:Porphobilinogen Synthase