Fluorimetric determination of DNA in papain digests of cartilage, using ethidium bromide

A fluorimetric procedure for the determination of the DNA content of cartilage is described. The tissue is initially solubilised by digestion with papain, and ethidium bromide is used for the subsequent quantitation of DNA. The basis of the procedure is the enhancement of fluorescence which occurs when ethidium bromide complexes with native nucleic acids, fluorescence due to DNA being distinguished from that due to RNA through the use of ribonuclease. The method provides reproducible results, allowing determination of DNA in papain digests containing greater than 1.25 microgram DNA/ml, and is a rapid alternative to more laborious colorimetric or fluorimetric methods, which require the separation of DNA from other tissue components. The procedure is highly specific for DNA and is useful in metabolic studies in which various parameters of chondrocyte activity are being studied.