Enzymatic Deacetylation of N-Acetylhistamine in Animal Tissues

Abstract

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 marked ly 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++ en hanced the activity at a low concentration and inhibited it at a high concentration. Cu++ Zn++, Hg++, Cd++ and p-chloromercuric benzoate (PCMB) inhibited the acti vity. The PCMB-inhibited activity was partially restored by the addition of gluta thione-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.

Properties of N‐Acetylhistamine Deacetylase in Mammalian Brain

“…Maximal activity for liver NAcHAD was 2,400 pmol HA/h/mg protein compared to 230 pmol HA/h/mg protein for brain NAcHAD. Endo and Ogura's (1975) K , for NAcHAD of NAcHA in brain supernatant was 10 times greater than our value and their reported K , value for a comparable liver enzyme source was three times our value. In a later study, Endo (1976) reported a K , of 300 FM NAcHA for partially purified NAcHAD from liver.…”

“…These data alone are not sufficient to rule out a neuronal function for NAcHAD. The intracellular localization results are different from those of Endo and Ogura (1975). They reported substantial NAcHAD activity in the 10,000 g pellet and almost no activity in the 1,000 g pellet.…”

“…The brain enzyme had a broad pH optimum between 8.3 and 8.9, whereas the liver NAcHAD had a sharp optimum at pH 8.3. Endo and Ogura (1975) reported similar pH profiles with the optimum at pH 8.0.…”

“…The coupled radioenzymatic assay we used in this study is approximately 1,000 times more sensitive than the fluorometric assay by Endo and Ogura (1975), as well as more rapid. When we originally described this assay (Hegstrand and Kalinke, submitted) we ran both the NAcHAD assay and the coupled HA assay which uses histamine N-methyltransferase (HNMT) at pH 8.0.…”