Lentil lectin enriched microsomes from the plasma membrane of the human B-lymphocyte cell line H2LCL carry a heavy load of type-1 porin

Using an established biochemical approach, five subcellular fractions of hu man B lymphocytes were prepared by differential centrifugation. Crude membr anes were passed over a lentil lectin column to enrich carbohydrate-coated cell surface microsomes. The lectin-bound fraction contained a high amount of plasma membrane-derived microsomes as indicated by cell surface markers. All subcellular fractions in Western blots proved to contain distinct but variable amounts of porin. There was a strong increase in porin content fro m crude membranes to plasma membrane-derived vesicles. The porin content of this fraction appeared to be higher than that of mitochondria. In the fina l step the plasma membrane-derived microsome fraction proved to be devoid o f contamination by outer mitochondrial membranes, as revealed by antibodies against the established markers MAO B and Tom20 applied in Western blots. These data prove the extramitochondrial expression of human type-1 porin/ty pe-1 VDAC.