Isocitric acid (HOOC-CHOH-CH(-COOH)-CH₂-COOH) is an intermediate of the Krebs TCA cycle, positioned between citrate and α-keto-glutarate. It is the branch point from which the glyoxylate shunt operates in plants and lower organisms. Isocitrate is found in substantial concentrations in many fruits and vegetables as well as in foods produced from these raw materials. In the TCA cycle, isocitrate is oxidized by isocitrate dehydrogenase (IDH) to α-ketoglutarate with the generation of NAD(P)H. Loss of NAD-IDH has been implicated as a potential causative factor in retinitis pigmentosa. BioVision's Isocitrate Assay Kit provides a simple, sensitive and rapid means of quantifying isocitrate in a variety of samples. In the assay, isocitrate is oxidized with the generation of NADPH which converts a nearly colorless probe to an intensely colored species with a λ_max of 450 nm. The Isocitrate Assay Kit can detect 1 to 20 nmoles (~20 mM) of isocitrate in various samples.