Enzymology — When the hexasaccharide substrate (NAG)6 is hydrolyzed by human lysozyme, what are the principal oligosaccharide products formed?

Introduction:Human lysozyme is a muramidase that cleaves beta-1,4 linkages between N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) in peptidoglycan; it can also act on defined NAG oligomers. This question focuses on the product profile when the model substrate (NAG)6 is hydrolyzed.

Given Data / Assumptions:

• Lysozyme has subsites that bind several sugar residues simultaneously, positioning one glycosidic bond for hydrolysis.
• (NAG)6 denotes a linear hexamer of N-acetylglucosamine residues.
• Cleavage typically yields a tetrasaccharide plus a disaccharide under standard conditions.

Concept / Approach:Consider lysozyme’s active-site subsites (A–F). When (NAG)6 occupies these, the scissile bond between the D and E subsites is hydrolyzed, producing a 4-mer and a 2-mer as the predominant products.

Step-by-Step Solution:

Verification / Alternative check:Chromatography of reaction mixtures shows peaks corresponding mainly to NAG4 and NAG2 after lysozyme digestion of (NAG)6.

Why Other Options Are Wrong:

Common Pitfalls:Assuming lysozyme fully degrades oligomers to monomers in one step; ignoring the active-site subsite model that predicts specific cleavage sites.

Final Answer:NAG4 + NAG2.