Xanthurenic acid is an endogenous molecule derived from tryptophan degradation by indoleamine-2, 3-dioxygenase. Indoleamine-2, 3-dioxygenase is induced in infectious diseases by liposacharides, interferon-α, and superoxide radicals. Xanthurenic acid is enzymatically formed by transamination of 3-hydroxykynurenine by kynurenine-aminotransferase. Kynurenine-aminotransferase, has been cloned from mitochondria and cytoplasm . Xanthurenic acid accumulates with age in senile cataract. This acid leads to apoptotic-like cell death, its BH3 domain in the cytoplasm being responsible for targeting the protein to mitochondria, resulting in cytochrome c release. Proteins with a BH3-domain (Bax, Bak, Bcl-xs, Bad) are transformed in the presence of xanthurenic acid to their proapoptotic-inducing state and translocated to mitochondria. In vitro, xanthurenic acid leads to covalent oligomerization of Bax, and Bcl-xs.
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