Histidine ammonia-lyase from rat liver. Purification, properties, and inhibition by substrate analogues.
Histidine ammonia-lyase (EC 4.3.1.3) from rat liver was purified more than 250-fold to near homogeneity. Electrophoretic determinations indicated a native molecular weight of approximately 200,000. The enzyme has a pH optimum of approximately pH 8.5. The minimum Km for L-histidine was 0.5 mM at pH 9.0. The Michaelis constant in the physiological pH range was, however, more than 2.0 mM. D-alpha-hydrazinoimidazolylpropionic acid was found to be a potent competitive inhibitor of liver histidine ammonia-lyase (Kis=75 muM); the L enantiomer of this compound was less effective in this regard. The enzyme was also inhibited competitively by L-histidine hydroxamate (Kis=0.4 mM), and to a lesser extent by L-histidinol, D-histidine, and glycine. Failure of a wide variety of other histidine analogues to inhibit the enzyme substantially indicates high specificity of the active site for L-histidine. No alternate substrates were identified for the enzyme. DL-alpha-Hydrazinophenylpropionic acid, the alpha-hydrzino analogue of phenylalanine, was similarly shown to be a very potent competitive inhibitor of a mechanistically similar L-phenylalanine ammonia-lyase purified from Rhodotorula glutinis. The properties of histidine ammonia-lyase from rat liver differ significantly from those of the enzyme from Pseudomonas fluorescens which has been studied most extensively to date.
D000642:Ammonia-Lyases / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D005260:Female; D006639:Histidine / Q000031:analogs & derivatives; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D008433:Mathematics; D010649:Phenylalanine; D011485:Protein Binding; D051381:Rats; D013329:Structure-Activity Relationship
D010649:Phenylalanine; D006639:Histidine; D000642:Ammonia-Lyases