From individual academic laboratories to Big Pharma manufacturing plants, small- and large-scale protein purification usually requires some type of liquid chromatography. Most purification techniques have been in use for decades, but the development of new resins has improved the time-tested methods that exploit proteins' physical and chemical properties to effect separations. This profile examines four techniques—gel filtration (GF), ion exchange (IEX), hydroxyapatite (HAP), and hydrophobic interaction (HI) chromatography. Affinity chromatography and HPLC (high-performance liquid chromatography) will be discussed in future articles.

For the novice protein purifier, finding a place to start might seem overwhelming, but fortunately the process can be approached systematically. Andrew Mitchell, technical consultant for Amersham Biosciences in Piscataway, NJ, explains that protein purification by liquid chromatography generally takes place in three phases: a capture step, in which the desired protein is separated from other cellular components such as DNA and RNA; an intermediate step, in which...

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