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 [ 3 H]inositol(1,3,4,5) tetrakisphosphate, with nanomolar affinity (K p = 90 nM) and a density of 250 fmol/mg protein. The specificity of the binding sites for Ins(1,3,4,5) P 4 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) P 4 was over 200-fold greater than for Ins(1,4,5) P 3 . The possibility is discussed that this binding site represents the receptor which mediates the action of Ins(1,3,4,5) P 4 as a putative intracellular second messenger.