Actinomycin D (1 mm in DMSO)

Prepare a solution of 1 mg actinomycin D (Sigma-Aldrich A1410) in 816 µL of DMSO (Sigma-Aldrich D2650). Determine the exact concentration of stock actinomycin D by measuring the absorbance at 441 nm and applying Beers law:

• Actinomycin D has a molar extinction coefficient of 21,900 (in water). The light path will depend on the spectrophotometer used to measure the absorbance at 441 nm. This is generally 1 cm when using older-style machines with cuvettes, but can be shorter (<1 mm) in modern machines such as the NanoDrop.

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