Semisynthesis iii - the homoserine 12,105 analogue of hen egg-white lysozyme.

The homoserine ^12,105 analogue of Hen egg-white lysozyme has been prepared by two routes. In the first approach a large excess of cyanogen bromide was used to cleave the native enzyme at methionines 12 and 105, the tertiary structure being maintained by the presence of the four disulphide bonds. Formation of the two new amide bonds was achieved using the activation of the homoserine lactone residues generated at positions 12 and 105; the reaction being most efficient when anhydrous DMSO was used as the solvent. An alternative approach using limited (two-fold excess) cyanogen bromide digestion gave the same homoserine analogue without chain fragmentation. A purified sample of the analogue showed no enzymic activity.