Hydrolysis of 4-methylumbelliferyl tetra-N-acetyl-β-chitotetraoside by lysozyme and its inhibition by N,N',N''-triacetylchitotriose

Article abstract of DOI:10.1248/cpb.32.3607

The hydrolytic activity of lysozyme towards 4-methylumbelliferyl tetra-N-acetyl-β-chitotetraoside (4-MU-(GlcNAc)₄) was little affected by ionic strength, though the activity of lysozyme towards cell suspension of Micrococcus lysodeikticus varied markedly with ionic strength. About 40-60% of lysozyme activity with 4-MU-(GlcNAc)₄ as a substrate was inhibited by 0.1 mM N,N',N''-triacetylchitotriose ((GlcNAc)₃), but the lytic activity of lysozyme towards M. lysodeikticus was little affected. The kinetics of hydrolysis of 4-MU-(GlcNAc)₄ by hen eggwhite (HEW) lysozyme and human placental (HP) lysozyme and the inhibition of this hydrolysis by (GlcNAc)₃ were investigated. The K(s) values for 4-MU-(GlcNAc)₄ of HEW- and HP-lysozymes were 19.7 and 27.9 μM, respectively, and the V(max) values were 0.124 and 0.0833 nmol/min/mg, respectively. The k values of both enzymes were very low, implying a poor orientation of the scissile bond in the substrate molecule with respect to the active site of lysozyme. (GlcNAc)₃ inhibited lysozyme with hyperbolic mixed-type inhibition. The inhibition reduced V(max) values of both lysozymes. The K(s) value of HEW-lysozyme was increased by the addition of the inhibitory whereas the K(s) value of HP-lysozyme was decreased. The K(i) value was 29.6 μm for HEW-lysozyme and 106 μM for HP-lysozyme.

Full text of DOI:10.1248/cpb.32.3607

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