A mammalian beta-hexosaminidase isoform that is a heteromeric protein comprized of both hexosaminidase alpha and hexosaminidase beta subunits. Deficiency of hexosaminidase a due to mutations in the gene encoding the hexosaminidase alpha subunit is a case of tay-sachs disease. Deficiency of hexosaminidase a and hexosaminidase b due to mutations in the gene encoding the hexosaminidase beta subunit is a case of sandhoff disease.