PLASMA-MEMBRANE INOSITOL 1,4,5-TRISPHOSPHATE RECEPTOR OF LYMPHOCYTES - SELECTIVE ENRICHMENT IN SIALIC-ACID AND UNIQUE BINDING-SPECIFICITY

The inositol 1,4,5-trisphosphate receptor (IP3R) associated with plasm a membranes of lymphocytes differs in terminal sugar content and bindi ng specificity from the cerebellar receptor, which is localized to end oplasmic reticulum. Lectin column chromatography reveals that 30% of I P3R in the thymus contains sialic acid, reflecting a plasma membrane a ssociation, in contrast to 5% of cerebellar IP3R. IP3R in thymus and p lasma membrane fractions of Jurkat lymphocytes differs from IP3R of Ju rkat microsomes and cerebellum in inositol phosphate specificity. The plasma membrane IP3R has lower affinity for IP3 but higher affinity fo r inositol 1,3,4,5-tetrakisphosphate, which may reflect a unique regul ation of calcium at the plasma membrane by inositol phosphates.