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.

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.