Crystalline L-histidine ammonia-lyase of Achromobacter liquidum. Crystallization and enzymic properties

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.