Immobilization of Enzymes Acting on Macromolecular Substrates: Reduction of Steric Problems
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Substrates of small molecular size can reach the active site of immobilized enzymes without suffering significant steric hindrances generated by the support. The situation is very different when macromolecular substrates are used (Fig. 1 ). Some of these reactions are of great interest; for example, hydrolysis of starch by amylases, limited proteolysis catalyzed by proteases, and hydrolysis of RNA or DNA by nucleases. Immobilized proteins for affinity chromatography (protein A, antibodies, and so on) are a further example in which the interaction may involve a macromolecule ( 1 ). In this chapter, we present three different strategies to reduce the steric problems associated with immobilized enzymes:
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Use of supports with different internal morphology;
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Preparation of enzyme derivatives with different orientations of the enzyme molecule on the support;
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Use of adequate spacer arms.
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Fig. 1. Steric problems in processes catalyzed by immobilized enzymes. When immobilized enzymes act on macromolecular substrates, the presence of the support surface can strongly restrict the access of those substrates to the enzyme active center.
