Partial purification and properties of N-acetylhistamine deacetylase

The enzyme catalyzing the deacetylaction of N-acetylhistamine was partially purified about 160-fold from rat liver extract and its properties were investigated. The purification procedure included DEAE-cellulose chromatography, precipitation with ammonium sulfate and DEAE-cellulose rechromatography. The enzyme contains a labile -SH group that is essential for its activity. Mn2+ and Co2+ enhanced the deacetylation reaction at low concentration. The molecular weight of the deacetylase was estimated to be about 70 000 from gel-filtration. Among various acetyl derivatives tested so far, N-acetylhistamine and to a lesser extent N-acetyltyramine served as the substrates. The Km value was 0.3 mM at the optimum pH 8.0 for N-acetylhistamine. Diphenhysramine, an antihistaminergic agent, inhibited the deacetylation remarkably.