Phalloidin-Atto 590

Atto 590 is a novel fluorescent label that belongs to the class of Rhodamine dyes. It shows a strong absorption, high fluorescence quantum yield, high thermal and photostability, and a very little triplet formation. Atto 590 consists of a mixture of two isomers with practically identical optical absorption and emission Phalloidin is a fungal toxin isolated from the poisonous mushroom Amanita phalloides. Its toxicity is attributed to the ability to bind F actin in liver and muscle cells. As a result of binding phalloidin, actin filaments become strongly stabilized. Phalloidin has been found to bind only to polymeric and oligomeric forms of actin, and not to monomeric actin. The dissociation constant of the actin-phalloidin complex has been determined to be on the order of 3 x 10^-8. Phalloidin differs from amanitin in rapidity of action; at high dose levels, death of mice or rats occurs within 1 or 2 hours. Fluorescent conjugates of phalloidin are used to label actin filaments for histological applications. Some structural features of phalloidin are required for the binding to actin. However, the side chain of amino acid 7 (g-d-dihydroxyleucine) is accessible for chemical modifications without appreciable loss of affinity for actin.

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