Understanding enzyme action at solid surfaces.

In solid-phase synthesis, there is interest in using enzymes that normally act on dissolved substrates. It is normally observed that rates and yields are substantially reduced when the usual substrates are covalently attached to a solid particle. Recently, there has been some progress in understanding the reasons for this, and hence how to improve behaviour. Diffusion of enzyme molecules into some of the support particles used in solid-phase chemistry is slow or absent. Methods are now available to visualize the sites of reaction, and hence detect this problem, and identify better support materials. Chemical equilibrium positions for reactions at the surface can be substantially altered compared with those in solution, so may unexpectedly limit yields. The shift can also be exploited to carry out, for example, direct synthesis of peptide bonds in an aqueous environment. The rate of enzyme attack depends on how the substrate moiety is attached to the surface, with an optimal 'spacer' length.