Molecular forms of beta-N-acetylhexosaminidase in Epstein-Barr virus-transformed lymphoid cell lines from normal subjects and patients with Tay-Sachs disease.

Abstract

In whole leukocytes and in lymphocytes from normal subjects, the percentage activity of heat-stable beta-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 beta-N-acetylhexosaminidase was almost completely heat-stable (95 - 98%). In the transformed cells from normal subjects, the beta-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. 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). 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. Hydrolytic properties using the both substrates (4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside and 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-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.