The docking of IP to its receptor, which is called the inositol trisphosphate receptor (InsP3R), was first studied using deletion mutagenesis in the early 1990s. Studies focused on the N-terminus side of the IP receptor. In 1997 researchers localized the region of the IP receptor involved with binding of IP to between amino acid residues 226 and 578 in 1997. Considering that IP is a negatively charged molecule, positively charged amino acids such as arginine and lysine were believed to be involved. Two arginine residues at position 265 and 511 and one lysine residue at position 508 were found to be key in IP docking. Using a modified form of IP, it was discovered that all three phosphate groups interact with the receptor, but not equally. Phosphates at the 4th and 5th positions interact more extensively than the phosphate at the 1st position and the hydroxyl group at the 6th position of the inositol ring.