Studies of Fc gamma receptors of human B lymphocytes: phospholipase A2 activity of Fc gamma receptors.
The presence of phospholipase A2 activity within human B cell Fc gamma receptors was investigated. Lysate produced by detergent treatment of chronic lymphocytic leukemia cells that had 1% of the cells surface radioiodinated was subjected to affinity chromatography by using either rac-1-(9-carboxynonyl)-2-hexadecylglycero-3-phosphorylcholine-Sepharose (PC-Sepharose) or heat-aggregated human IgG-Sepharose 4B conjugate (IgG-Sepharose). The materials eluted from both adsorbants by ethylenediaminetetraacetate- or urea-containing buffer were further purified by gel filtration and isoelectric focusing in the presence of 6 M urea. Both isolated PC- and IgG-binding materials were homogeneous, when judged by gel filtration and isoelectric focusing, and had identical isoelectric points (pI = 6.5), peptide maps, and amino acid compositions. Furthermore, both preparations catalyzed equally the hydrolysis of phosphatidylcholine to release fatty acid from the 2 position. Optimal enzymatic activity depended on the presence of Ca2+, was maximal at pH 9.5, and was augmented by Fc gamma fragments. Both preparations specifically bound to the Fc portion of IgG and inhibited human antibody-coated erythrocyte rosette formation by peripheral mononuclear cells. Our data thus demonstrate the identity of PC- and IgG-binding materials and suggest that a functional activity of the human B cell Fc gamma receptor is the generation of phospholipase A2 activity within the plasma membrane.
D000596:Amino Acids / Q000032:analysis; D001402:B-Lymphocytes / Q000201:enzymology*; D002462:Cell Membrane / Q000201:enzymology; D002846:Chromatography, Affinity; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D007525:Isoelectric Focusing; D007945:Leukemia, Lymphoid / Q000201:enzymology; D010740:Phospholipases / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011961:Receptors, Fc / Q000378:metabolism
D000596:Amino Acids; D007074:Immunoglobulin G; D011961:Receptors, Fc; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2