The GM2-activator protein (GM2AP) is an essential cofactor for the degradation of ganglioside GM2 by lyso-somal b-hexosaminidase A. It mediates the interaction between the water-soluble exohydrolase and its membrane-bound substrate at the lipid–water interphase. Inherited defects in the gene encoding this glycoprotein result ina fatal neurological storage disorder, the AB variant of GM2-gangliosidosis. To elucidate the mode of action of this gly-coprotein cofactor, we synthesized the two photoaffinity labels [ 14 C]C3 -TPD-GM2 and [ 14 C]C7 -TPD-GM2. .
