Tricarballylic acid, a conjugate acid of a tricarballylate, is a competitive inhibitor of the enzyme aconitate hydratase (aconitase; EC 4.2.1.3) with a Ki value of 0.52 mM[2]. Tricarballylic acid, an inhibitor of ATP-citrate lyase, blocked the ability of citrate to augment TNF-α, linking citrate's augmentation effect with its metabolism by ATP-citrate lyase. In the presence of citrate, increased histone acetylation was observed in the TNF-α and IL-8 promoter regions of THP-1 cells[3]. Tricarballylic acid (a substrate analogue of D-isocitric acid) gives competitive inhibition versus D-isocitrate at all NADP levels and mixed inhibition versus NADP, at sub-saturating levels of D-isocitrate[4]. Tricarballylic acid is a non-metabolizable rumen bacterial fermentation product of the naturally occurring tricarboxylic acid trans-aconitic acid. Citrate as well as tricarballylate uptake (at a concentration of 0.05 mmol l-1) was strongly stimulated by an inwardly directed initial Na+ gradient. Unequivocal evidence for a common transport site for tricarballylate and citrate was obtained from 'cis-inhibition' and 'trans-stimulation' of Na(+)-dependent citrate uptake by tricarballylate. Tricarballylate and citrate are transported across the intestinal brush-border membrane by a common, Na(+)-dependent transport mechanism[5].
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