Human serum contains a chitinase: identification of an enzyme, formerly described as 4-methylumbelliferyl-tetra-N-acetylchitotetraoside hydrolase (MU-TACT hydrolase)

Since 1988 an endoglucosaminidase, provisionally named MU-TACThydrolase, has been known that hydrolyses the artificial substrate4-methylumbelliferyl-tetra-N-acetyl-chitotetraoside (MU-GlcNAc]₄,where GlcNAc is N-acetyl-glucosamine). The biological functionof the enzyme was unknown. In this paper evidence is presentedshowing that this endoglucosaminidase from human serum is infact a chitinase that is different from lysozyme. The factssustaining this finding are: (i) the identification of the productsformed from MU-GlcNAc]₃ as GlcNAc]₂ and GlcNAc]₃; (ii) chitinand ethylene glycolchitin can be degraded by the enzyme; (iii)the chitinase inhibitor allosamidin also inhibits the actionof MU-TACT hydrolase from human serum; (iv) no hydrolysis ofthe lysozyme substrate Micrococcus lysodeikticus. The enzymealso occurs in rat liver. It was demonstrated that upon Percolldensity gradient centrifugation the enzyme from this tissuedistributed parallel to the lysosomal marker enzymes ß-N-acetylhexosaminidaseand ß-galactosidase, indicating a lysosomal localizationfor this enzyme. It is proposed that the enzyme functions inthe hydrolysis of chitin, to which mammals are frequently exposedduring infection by pathogens. allosamidin chitinase human serum lysozyme MUTACT hydrolase