Lysozyme (EC 3.2.1.17) is a crucial enzyme with complex interactions involving its carboxyl and amino groups.
Understanding these interactions is key to elucidating enzyme function and stability.
Identifying abnormal pK values of residues provides insights into the enzyme's microenvironment.
Purpose of the Study:
To investigate the interaction between carboxyl and amino groups in native lysozyme.
To identify the specific positions and pK values of abnormal carboxyl groups.
To characterize the titratable residues in native and N-acetylated lysozyme.
Main Methods:
Preparation of N-acetylated lysozyme to selectively modify amino groups.
pH titration of native and N-acetylated lysozyme in aqueous KCl solutions.
Spectrophotometric titration to assess tyrosine residue titratability.
Main Results:
Acetylation modified six amino groups, leaving Lys 33 as the sole titratable amino group.
pH titration revealed fewer titratable groups in acetylated lysozyme, with abnormal carboxyl groups identified at Asp 48, Asp 66, and Asp 87.
Spectrophotometric titration showed all three tyrosine residues are titratable in acetylated lysozyme, with Tyr 20 being untitratable in native lysozyme within the pH range of 8-12.6.
Conclusions:
Specific carboxyl groups (Asp 48, 66, 87) exhibit abnormal pK values in native lysozyme due to interactions with other residues.
Lys 33 is the primary titratable amino group in N-acetylated lysozyme.
Tyr 20's untitratability in native lysozyme suggests a unique microenvironment influencing its ionization.