Hydroxylase inhibitory action

An enzyme inhibitor of microbial origin with a simple structure, fusaric acid (XXXIV), is a hypotensive agent. This compound has been tested clinically as the free acid (29) and as the calcium salt (30) and is orally effective in man with a low incidence of side-effects. Dopamine-p-hydroxylase inhibitory action of this compound has been demonstrated in man (29). 

In biological systems, therefore, the behavior of Li+ is predicted to be similar to that of Na+ and K+ in some cases, and to that of Mg2+ and Ca2+ in others [12]. Indeed, research has demonstrated numerous systems in which one or more of these cations is normally intrinsically involved, including ion transport pathways and enzyme activities, in which Li+ has mimicked the actions of these cations, sometimes producing inhibitory or stimulatory effects. For example, Li+ can replace Na+ in the ATP-dependent system which controls the transport of Na+ through the endoplasmic reticulum Li+ inhibits the activity of some Mg2+-dependent enzymes in vitro, such as pyruvate kinase and inositol monophosphate phosphatase Li+ affects the activity of some Ca2+-dependent enzymes— it increases the levels of activated Ca2+-ATPase in human erythrocyte membranes ex vivo and inhibits tryptophan hydroxylase. 

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