Specific binding sites for [3H]inositol(1,3,4,5)tetrakisphosphate on membranes of HL-60 cells

Membranes of HL-60 cells were shown to possess saturable binding sites for [3H]inositol(1,3,4,5)tetrakisphosphate, with nanomolar affinity (KD = 90 nM) and a density of 250 fmol/mg protein. The specificity of the binding sites for Ins(1,3,4,5)P4 was assessed by competition studies utilising a variety of inositol polyphosphates; results indicated that both the presence and the correct grouping of the phosphates were important for high affinity recognition. The apparent affinity of the binding sites for Ins(1,3,4,5)P4 was over 200-fold greater than for Ins(1,4,5)P3. The possibility is discussed that this binding site represents the receptor which mediates the action of Ins(1,3,4,5)P4 as a putative intracellular second messenger.