Human lymphocyte membrane proteins treated with neuraminidase

Human peripheral blood lymphocytes were surface-iodinated, treated with neuraminidase from Vibrio cholerae and lysed with non-ionic detergent. In addition, surface membrane fractions were isolated from surface-iodinated cells in the absence of detergents and treated with neuraminidase after membrane isolation. The effect of neuraminidase treatment on the membrane proteins was studied by two-dimensional gel electrophoresis. One surface-labelled protein of 45 000 molecular weight which is characterized by its association with the detergent-resistant matrix of the cells and by its specific enrichment in an isolated membrane fraction, was found to be particularly sensitive to neuraminidase treatment both of intact cells and isolated membranes. A prominent labelled protein of apparent molecular weight of 60 000 is observed in the soluble fraction after neuraminidase treatment of intact cells. The analogous protein is detected when isolated membrane fractions are treated with neuraminidase.