obsolete inositol pyrophosphate synthase activity true inositol diphosphate synthase activity OBSOLETE. Catalysis of the phosphorylation of inositol phosphates which possess diphosphate bonds. molecular_function inositol pyrophosphate synthase activity GO:0000826 This term was made obsolete because it is incorrectly defined; 'inositol pyrophosphate' is a inositol derivative to which one (or more) pyrophosphate moieties are attached. 'Inositol pyrophosphate synthase' refers to a class of enzymes that catalyze various different reactions that result in the formation of an IP, so one cannot formulate a general reaction for them.