Abstract
The addition of both native and boiled 105000 g supernatant from rat liver to dopamine β-hydroxylase assay system caused marked decreases in dopamine β-hydroxylase activity, and the degrees of these inhibitions were dose-dependent. When the boiled supernatant was fractionated by using chromatography on a Sephadex G-25 superfine, at least two inhibitory peaks were observed by the addition of each column fraction. The second inhibitory peak (fraction 26) was estimated to have a molecular weight of about 1000-1300. This inhibition was non-competitive with substrate, tyramine and co-substrate, ascorbic acid and completely reversed by the addition of sulfhydryl reactive agents such as N-ethylmaleimide. The second inhibitory peak coincided to the peak of the stimulation of adenyl cyclase of rat brain synaptosomes by the addition of column effluent of a Sephadex G-25 superfine.
