Histidine ammonia-lyase from rat liver. Purification, properties, and inhibition by substrate analogs

Publisher Website
Google Scholar
Abstract
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 MW of .apprx. 200,000. The enzyme has a pH optimum of .apprx. pH 8.5. The minimum Km for L-histidine was 0.5 mM at pH 9.0. The Km in the physiological pH range was more than 2.0 mM. D-.alpha.-Hydrazinoimadazolylpropionic acid was a potent competitive inhibitor of liver histidine ammonia-lyase (Kis = 75 .mu.M); 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 analogs 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.-hydrazino analog of phenylalanine, was 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.