Lysozyme methylated derivative

Various modification products have been isolated by chromatography on Amberlite CG-50 of a mixture of A-carboxymethylated derivatives of lysozyme. In each carboxymethyl derivative the position of the modified amino-acid was established. It was found that L-histidine-15, L-lysines-1, -33, -96, or -97 are blocked, whereas L-lysines-13 and -116 remain unaffected. Possible causes of this selectivity were discussed. Salt activation of carboxy-methyl derivatives of lysozyme proceeds more readily the higher the degree of modification, and the enzymatic activity of carboxymethyl derivatives of lysozyme is higher than that of the native enzyme owing to their increased affinity for substrate (chitin). 

Table XXXI. On considering the large number of groups determined, the difference between the number of groups in the native and methylated lysozymes, 3.6 1.0, is in fairly good accord with the observed difference, 3.0 0.2, between the titrations of the native lysozyme in KCl and in GU. The data of Table XXXI also are in good accord with the analytical data of Jollfes and Jollfes (1959), who report 22 aspartic acid and 5 glutamic acid residues. These, together with the terminal carboxyl group, correspond fairly well with the 29 groups found in the methylated derivative, and seem to be consistent with the hypothesis that these extra groups in lysozyme are actually masked carboxylate ions.

The amino groups of ovomucoid, lysozyme, and ovotransferrin were alkylated extensively (40-100%) with various carbonyl reagents in the presence of sodium borohydride. Monosubstitution was observed with acetone, cyclopentanone, cyclohexanone, and benzaldehyde, while 20-50% disubstitution was observed with 1-butanal and nearly 100% disubstitution was observed with formaldehyde. The methylated and isopropylated derivatives of all three proteins were soluble and retained almost full biochemical activities. Recently amine boranes have been shown to be possible alternative reducing agents for reductive alkylation... 

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