Lysozyme, active site conformational change

Fig. 14. Active site region of lysozyme. The Ln(III), NMR study demonstrated the structure in solution and showed that Val 109 flips rapidly, that Trp 108 undergoes conformational changes, that Trp 62 flips and that Tyr 53 flips rapidly...

Firstly, not all enzymes exhibit activity in the crystal (e.g., lysozyme) because neighbouring molecules in the crystal lattice block access to the active site. Secondly, in those enzymes where a conformational change is an obligatory part of the reaction, a reduction in rate may be anticipated if these conformational changes cannot be accomplished readily in the crystal. Thirdly, there is a limitation imposed by diffusion of substrate into and products out of the crystal. Quiocho and Richards [167] showed that with carboxypeptidase Aj, crystals of 5 pm or less were required before the specific activity of the enzyme in the crystal became independent of crystal size. Rossi and Bernhard [168,169] studied the deacylation rate of co-crystallised acylated a-chymotrypsin using a chromophoric substrate. Under conditions where diffusion away of product was not essential for detection of reaction, they showed that deacylation rates were the same in the crystal as in solution. 

A carboxyethyl derivative of lysozyme and synthetic disulphide peptides have been used to study the enzymic and immunochemical properties of lysozyme around the disulphide bridge (linking residues 6—127) at the reactive site. One of the six tryptophanyl residues, possibly either tryptophan-62 or -63, of hen egg-white lysozyme has been oxidized selectively with ozone in aqueous solution. N -Formylkynurenine was formed, with concomitant loss of the enzymic activity, although there was apparently little change in the gross conformation of the molecule. 

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