The metabolic link between Ins(1,4,5)P3 and Ins(1,3,4,5,6)P5 in animal cells. The figure shows the quantitatively most important reactions in animal cells that link Ins(1,4,5)P3 to Ins(1,3,4,5,6)P5. Numbers in the figure refer to various enzymes as follows: 1. Ins(1,4,5)P3 3-kinase (EC 2.7.1.127); 2. Ins(1,4,5)P3/Ins(1,3,4,5)P4 5-phosphatase (EC 3.1.3.56); 3. ITPK1 (EC 2.7.1.134); 4. Inositol phosphate multikinase (EC 2.7.1.151); note that kinetic data have led to it being questioned whether IPMK can contribute significantly to Ins(1,3,4,5)P4 synthesis de novo in animal cells (Chang et al., 2002).