ENZYMATIC DEACETYLATION OF N-ACETYLHISTAMINE IN ANIMAL TISSUES

Abstract

N-Acetylhistamine-deacetylating activity was observed in all tissues tested of rats, mice and guinea-pigs. The liver, kidney, spleen and brain showed the high enzymatic activity. The major part of activity was localized in the cellular soluble fraction. In the brain, enzymatic activity was localized in a similar level in both the 100, 000 g supernatant and 10, 000 g sediment. The deacetylating activity was markedly increased by the addition of Mn⁺⁺. Na⁺, K⁺, Li⁺, Ca⁺⁺ and Mg⁺⁺ had no effect. The Mn⁺⁺ concentration optimum for the activity was in a range 0.5-1 mM. Co⁺⁺ enhanced the activity at a low concentration and inhibited it at a high concentration. Cu⁺⁺ Zn⁺⁺, Hg⁺⁺, Cd⁺⁺ and p-chloromercuric benzoate (PCMB) inhibited the activity. The PCMB-inhibited activity was partially restored by the addition of glutathione-SH or cysteine. The optimum pH of the enzymatic reaction was 8.0 in the presence of Mn⁺⁺. These properties were common among the enzymes in different tissues.