title: Crystalline L-histidine ammonia-lyase of Achromobacter liquidum. Crystallization and enzymic properties.
abstract: Crystalline L-histidine ammonia-lyase of Achromobacter liquidum was prepared with a 24% recovery of the activity. The specific activity of the pure enzyme (63 mumol of urocanic acid min-1 mg-1) is similar to those so far reported for the enzyme from other sources. The purified enzyme appeared to be homogeneous by analytical disc electrophoresis and isoelectric focusing (pI = 4.95). The molecular weight determined by Sephadex G-200 gel filtration is 200000. The optimum pH is 8.2, and the optimum temperature is 50 degrees C. The enzyme showed strict specificity to L-histidine (Km = 3.6 mM). Several histidine derivatives are not susceptible to the enzyme but do inhibit the enzyme activity competitively; the most effective inhibitors are L-histidine methyl ester (Ki = 3.66 mM) and beta-imidazole lactic acid (Ki = 3.84 mM). L-Histidine  hydrazide (Ki = 36 mM) and imidazole (Ki = 6 mM) noncompetitively inhibited the enzyme EDTA markedly inhibited enzyme activity and this inhibition were reversed by divalent metal ions such as Mn2+, Co2+ Zn2+, Ni2+, Mg2+, and Ca2+. These results suggest that the presence of divalent metal ions is necessary for the catalytic activity of histidine ammonia-lyase. Sodium borohydride and hydrogen peroxide inhibited the enzyme activity.
mesh_terms: D000421:Alcaligenes / Q000201:enzymology*; D000642:Ammonia-Lyases / Q000302:isolation & purification*; D002413:Cations, Divalent; D003460:Crystallization; D004492:Edetic Acid / Q000494:pharmacology; D006638:Histidine Ammonia-Lyase / Q000302:isolation & purification* / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007525:Isoelectric Focusing; D007700:Kinetics; D008970:Molecular Weight
chemical_list: D002413:Cations, Divalent; D004492:Edetic Acid; D000642:Ammonia-Lyases; D006638:Histidine Ammonia-Lyase