Fig. 4. A portion of GalT I partitions with detergent-resistant lipid rafts. (a) Nontransfected 3T3 fibroblasts were lysed in detergent and insoluble material isolated and applied at the bottom of Optiprep gradients. After equilibrium centrifugation, the lighter, caveolin-containing lipid rafts float to near the top of the gradient (fraction 2), whereas membrane and matrix proteins (GM130, p115) not associated with lipid rafts remain in the heavier density fractions near the bottom of the gradient (fraction 10,11). The long GalT I isoform is found in both the detergent-insoluble fractions and the caveolin-containing lighter lipid rafts. (b) When the entire detergent-treated cell lysate (i.e. detergent soluble and insoluble pools) was subjected to the gradient, a larger percentage of the total cellular GalT I remained at the bottom of the gradient, as assayed with antibodies that recognize both GalT I isoforms (i.e. anti-GalT I catalytic domain). This is consistent with the presence of an additional pool of GalT I that is detergent-soluble, and therefore not associated with lipid rafts.

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