Molecular Forms of β‐ N ‐Acetylhexosaminidase in Epstein‐Barr Virus‐Transformed Lymphoid Cell Lines from Normal Subjects and Patients with Tay‐Sachs Disease

1 In whole leukocytes and in lymphocytes from normal subjects, the percentage activity of heat‐stable β‐ N ‐acetylhexosaminidase (30 ± 5% and 45 ± 5%, respectively) was higher than in the transformed lymphoid cell line (19 ± 3%). In Tay‐Sachs transformed cells as well as non‐transformed lymphocytes, β‐ N ‐acetylhexosaminidase was almost completely heat‐stable (95–98%). 2 In the transformed cells from normal subjects, the β‐ N ‐acetylhexosaminidase B (Hex B) activity (5% of total) was significantly lower than in blood lymphocytes (average 25–30% of total activity), whereas Hex A and Hex I were similar in the either cell type. 3 Blood lymphocytes and lymphoid cell lines established from a Tay‐Sachs patient lacked heat‐labile Hex A and expressed high heat‐stable Hex I and Hex B activities (3–6‐fold). 4 After neuraminidase treatment, Hex A peak sharpened while Hex I peaks switched to higher pI than normal Hex I, in the region of Hex B. PreHex A/S pI was not affected. 5 Hydrolytic properties using the both substrates (4‐methylumbelliferyl‐2‐acetamido‐2‐deoxy‐β‐ d ‐glucopyranoside and 4‐methylumbelliferyl‐2‐acetamido‐2‐deoxy‐β‐ d ‐galactopyranoside) of each molecular form were similar in transformed and non‐transformed cells. Data derived from the use of a mixture of substrates were consistent with the model which proposes a common active site for either substrate in the case of preHex A, Hex B and Hex I, but not for Hex A. Thus Epstein‐Barr virus‐transformed lymphoid cell lines represent an accurate model system for studies on Tay‐Sachs disease.