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Proteinase K

Proteinase K, a broad-spectrum serine protease, is widely used in molecular biology for the isolation of nucleic acids. It was discovered in 1974 and was extracted from fungus, Tritirachium album. The name “Proteinase K” comes from the ability of the enzyme to digest hair or keratin. Activated by calcium, the enzyme digests proteins preferentially adjacent to the carboxyl group of aliphatic and aromatic amino acids. Although calcium is not necessary to maintain the enzyme activity, they do contribute to enzyme stability. Upon removal of the calcium ions, the stability of the enzyme is reduced, and the proteolytic activity is partially lost. Proteinase K has two binding sites for Ca2+, which is located close to the active center, but is not directly involved in the catalytic mechanism. The enzyme is stable over a wide range of pH from 7.5 - 12, with an optimum pH at 8.0. The enzyme is active at 37°C and the activity increases with temperature up to 60°C. Proteins will be completely digested if the incubation time is extended and if the protease concentration is very high. Therefore, it is important to find the optimum incubation time that is specific for each sample type.

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