AN ENZYME WITH PROPERTIES SIMILAR TO THOSE OF BETA-N-ACETYLHEXOSAMINIDASE S IS EXPRESSED IN THE PROMYELOCYTIC CELL-LINE HL-60

Extracts of the human promyelocytic cell line HL-60 contain a form of β-N-acetylhexosaminidase that is not retained on columns of benzeneboronate-agarose ('phenylboronate-agarose') and has a pI value lower than that of β-N-acetylhexosaminidase A. It is clearly distinct from β-N-acetylhexosaminidase A in its behaviour on DEAE-cellulose columns, and it requires a higher concentration of salt for its elution. This 'extra' form has a higher ratio of activity towards 4-methylumbelliferyl β-N-acetylglucosaminide 6-sulphate and 4-methylumbelliferyl β-N-acetyglucosaminide than has β-N-acetylhexosaminidase A and is less stable when heated at 50°C. It has a pH optimum of 4.5 and is therefore not β-N-acetylglucosaminidase C. Anti-(human β-N-acetylhexosaminidase α-subunit) serum precipitated both β-N-acetylhexosaminidase A and the 'extra' form, whereas an anti-(β-subunit) serum precipitated β-N-acetylhexosaminidase A but not the 'extra' form. Western blotting and immunodetection of polypeptides derived from the 'extra' form revealed a band corresponding in size to mature α-subunits. On the basis of this and of its behaviour on isoelectric focusing, chromatofocusing and its kinetic properties, we conclude that the 'extra' form is composed of α-subunits and resembles β-N-acetylhexosaminidase S, the residual form in Sandhoff's disease.