ABSTRACT
PHYTATE (myo-inositol hexakisphosphate, InsP6) is a common constituentof plants, largely stored as a complex salt of Mg2+, K+, and proteins within subcellular single-membrane particles (globoids, aleurone grains) in grains and seeds. As much as 60-80% of the phosphorus present in such organs may be InsP6 [35,36,55]. Other cations including Ca2+, Zn2+, Fe3+, and Cu2+ are usually present in measurable quantities. More recently, significant amounts of InsP6 have been found to occur in protista and higher animals, including humans wherein this compound may have significant functions involving signal transduction and cellular regulation [57,63]. This chapter on the biosynthesis of phytic acid begins with an introduction to the biosynthesis of myo-inositol, the carbocyclic structure of InsP6. An overview of myo-inositol mono-and polyphosphates follows. Because specific Ins(n)Pns are involved in discrete processes leading to signal-transducing polyphosphates [Ins(1,4,5)P3, Ins(1,3,4,5)P4, etc.], InsP6 biosynthesis, and InsP6 breakdown, each must be dealt with separately because intermediate phosphate esters are often unique. Finally, selected biochemical properties and functional aspects of phytic acid will be discussed.
