journal of biotechnology ELSEVIER Journal of Biotechnology 36 (1994)95-119 Minireview The affinity technology in downstream processing N. Labrou, Y.D. Clonis * Enzyme Technology Laboratory, Department of Agricultural Biology and Biotechnology, Agricultural University of Athens, lera Odos 75, 118 55 - Athens, Greece Received 21 October 1993; revisionaccepted 18 February 1994 Abstract The quality criteria imposed on several biochemicals are stringent, thus, high-separation purification technology is important to downstream processing. Affinity-based purification technologies are regarded as the finest available, and each one differs in its purifying ability, economy, processing speed and capacity. The most widely used affinity technology is classical affinity chromatography, however, other chromatography-based approaches have also been developed, for example, perfusion affinity chromatography, hyperdiffusion TM affinity chromatography, high-perfor- mance affinity chromatography, centrifugal affinity chromatography, affinity repulsion chromatography, heterobi- functional ligand affinity chromatography and the various chromatographic applications of 'affinity tails'. On the other hand, non-chromatographic affinity technologies aim at high throughput and seek to circumvent problems associated with diffusion limitations experienced with most chromatographic packings. Continuous affinity recycle extraction, aqueous two-phase affinity partitioning, membrane affinity filtration, affinity cross-flow ultrafiltration, reversible soluble affinity polymer separation and affinity precipitation are all non-chromatographic technologies. Several types of affinity ligands are used to different extents; antibodies and their fragments, receptors and their binding substances, avidin/biotin systems, textile and biomimetic dyes, (oligo)peptides, antisense peptides, chelated metal cations, lectins and phenylboronates, protein A and G, calmodulin, DNA, sequence-specific DNA, (oligo)nucleotides and heparin. Likewise, there are several support types developed and used; natural, synthetic, inorganic and composite materials. Key words: Downstream processing; Bioseparation; Enzyme purification; Biocatalyst purification; Affinity technol- ogy; Affinity chromatography; Affinity ligand; Affinity adsorbent; Dye ligand I. Introduction The key-factor for the commercial develop- ment of biotechnology is downstream processing, which purifies bioproducts and often accounts for * Corresponding author. at least 50% of total costs. Critical steps in down- stream processing are the 'high-separation' tech- nologies, of which chromatography is the most widely used. However, where substantial purity is necessary, for example, with molecular biology, diagnostic and therapeutic proteins, the finest of technologies is often employed: affinity chro- matography (Cuatrecasas and Anfinsen, 1971; Lowe, 1979; Clonis, 1987a; Clonis and Lowe, 1988; 0168-1656/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0168-1656(94)00054-G