Avian red blood cells contain a millimolar amount of inositol polyphosphate which plays a role as an allosteric effector of hemoglobin. We confirmed the structure of this substance by NMR techniques as purely myo-inositol 1,3,4,5,6-pentakisphosphate. Based on present knowledge this effector is synthesized from inositol trisphosphate by successive phosphorylation. In a search for biosynthetic and degradative intermediates of inositol pentakisphosphate we found only one inositol tetrakisphosphate isomer. Its structure was unambiguously assigned by proton, 13C- and 31P-NMR to myo-inositol 1,4,5,6-tetrakisphosphate. As in mammalian cells the major inositol tetrakisphosphate isomer is myo-inositol 1,3,4,5-tetrakisphosphate, there seem to be differences between avian red blood cells and mammalian cells in the routes of inositol polyphosphate formation and/or degradation.
