inositoltetraphosphate

Inositol tetraphosphate, commonly abbreviated IP4, denotes a group of related esters in which four phosphate groups are covalently linked to the cyclic inositol ring. Because the inositol ring has six hydroxyl groups, IP4 exists in several stereoisomeric forms depending on which positions bear phosphate groups. In biological contexts, IP4 is usually discussed as an intermediate in the metabolism of inositol phosphates and as a precursor to higher inositol phosphates such as IP5 and IP6.

Biogenesis and metabolism: IP4 is formed from IP3 by the action of specific inositol phosphate kinases, notably inositol polyphosphate multikinase (IPMK) and related enzymes, and can be further phosphorylated to IP5 and IP6. It is also produced, and degraded, by phosphatases that remove phosphate groups. The relative abundance and specific isomer composition of IP4 can vary by cell type and physiological state.

Functions: In many eukaryotes, inositol phosphates act as signaling molecules that regulate diverse processes, including calcium release, vesicle trafficking, transcription, and enzyme activity. IP4, like other inositol phosphates, can modulate IP3 receptor activity or serve as a substrate for additional phosphorylation. However, due to the existence of multiple IP4 isomers and limited structural characterization, precise functional roles are variable and not fully defined, and research continues to delineate organism-specific roles.

See also: Inositol phosphates, IP3, IP5, IP6, IP7, IP8.