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 proteins are isolated from contaminants similar in size or other physical/chemical properties; and a polishing step, in which the sample is readied for use. Each purification stage has certain chromatography techniques and bead sizes that are best suited to it.
The initial capture step typically involves protein isolation from a crude cell lysate and requires a resin with a high capacity and high flow rate. "Fast flow" resins with a large bead size and large bead size range (the range can vary ...
