Plasma methylumbelliferyl-tetra-N-acetyl-chitotetraoside hydrolase: further study of its characteristics as a chitinase and comparison with its activity on Remazol Brilliant Violet carboxymethyl chitin.

W R Den Tandt, S Scharpé

Index: Clin. Chim. Acta 268(1-2) , 107-20, (1997)

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Abstract

We have further studied some characteristics of human plasma specific chitinase by making use of the fluorescent substrate methylumbelliferyl-tetra-N-acetyl-beta-D-chitotetraoside (MU-TACT). The enzyme is also active towards the substrates MU-di-N-acetyl-beta-D-chitobioside (MU-DACB) and MU-N-acetyl-chitotrioside (MU-TRACT). MU-TACT hydrolase in plasma is very stable. It is inhibited by the substrate and the product of the reaction and by allosamidin and ethyleneglycolchitin. When the activity of plasma MU-TACT hydrolase was compared to Remazol Brilliant Violet carboxymethyl (RBV) chitin hydrolase (RBV chitinase), it appeared that another enzyme--lysozyme--is also active on RBV chitin and this enzyme represents about 50-60% of the total RBV chitinase activity. Highly increased activity of plasma MU-TACT hydrolase in plasma of Gaucher patients was reflected in a similar increase of RBV chitin hydrolase. In these patients, both MU-TACT hydrolase and RBV chitinase are totally inhibited by allosamidin indicating that specific chitinase is the increased enzyme. With the MU-TACT substrate, specific chitinase is measured and with RBV chitin as substrate the measured activity is a combination of specific chitinase (activity inhibited by allosamidin) as well as lysozyme (residual activity after allosamidin inhibition). For measurement of specific chitinase in human plasma and clinical applications, the di-, tri- or tetra-N-acetylglucosamine derivatives of MU are recommended. In order to avoid confusion, recommended names are either the total substrate followed by -ase, or chitinase.