22-Hydroxytingenone from Glyptopetalum sclerocarpum had important effects on respiratory activity of isolated rat liver mitochondria. Initially, 22-hydroxytingenone uncoupled the mitochondria respiration which was followed by inhibition of state 4 respiration using NAD -linked substrate (glutamate + malate) or succinate. Its action had exhibited some characteristics of classical uncoupler - DNP, e.g., the ability to abolish the coupling of substrate oxidation and ATP synthesis, causing loss of respiratory control, lowering ADP/O ratio as well as RCI value, reversion of oligomycin inhibited state 3 respiration and activated the mitochondrial ATPase which was inhibited by oligomycin. However, this compound had some different effect from DNP, its uncoupling action was unaffected by varying pH of incubation medium from 7.2-7.6 and activating action on mitochondrial ATPase was not inhibited by atractyloside. The effect on respiration after uncoupling action, 22-hydroxytingenoçe inhibited mitochondrial state 3 state 4 respiration supported by NAD+ -linked substrate or succinate and state 3u respiration especially with NAD+ -linked substate but had no inhibitory effect when using ascorbate + TMPD. These results shown that 22-hydroxytingenone inhibited the complex I of respiratory chain rather than complex II. 22-Hydroxytingenone did not inhibit the mitochondrial monoamine oxidase activity. Its uncoupling and inhibiting respiration were reduced by bovine serum albumin and DTNB and completely antagonized by DTT, so the molecular mechanism of uncoupling action and inhibiting respiration may involve sulfhydryl group in mitochondrial inner membrane thus the mitochondria could be able to oxidize exogenous NADH.
