cisaconitic

cis-aconitic acid, commonly referred to as cis-aconitate, is the cis geometric isomer of aconitic acid. It is a tricarboxylic acid featuring a carbon–carbon double bond, and the cis designation refers to the arrangement of groups around that double bond. In biological contexts, cis-aconitate is typically discussed as an intermediate in its anionic or deprotonated form.

In metabolism, cis-aconitate is an intermediate of the citric acid cycle (Krebs cycle). Citrate is converted to cis-aconitate by the enzyme aconitase through a dehydration reaction, and cis-aconitate is subsequently hydrated to form isocitrate. This rearrangement prepares the molecule for oxidative decarboxylation later in the cycle. Aconitase, an iron-sulfur protein located in the mitochondrial matrix of most eukaryotic cells, catalyzes both steps. The process is reversible and subject to regulation according to cellular energy needs.

Chemical and physiological properties: cis-aconitate is highly polar and exists in multiple ionic forms depending on pH. In cells, it is typically short-lived, rapidly converted to isocitrate; its transient nature makes direct steady-state measurement challenging. In laboratory studies, cis-aconitate can be used to probe aconitase activity or to study flux through the citric acid cycle.

Relevance: as a key intermediate, cis-aconitate links citrate to isocitrate and helps drive the continuation of substrate oxidation in aerobic respiration. Its levels and turnover reflect the activity of the early citric acid cycle and the overall metabolic state of the cell.