Complete characterization of the myo-inositol polyphosphates from beef brain phosphoinositide.

The identification of a myo-inositol-containing phospholipid isolated from beef brain (1) as a triphosphoinositide has been reported in earlier publications from this laboratory (2) and in a note by Dittmer and Dawson (3). It has been established (2) by periodate oxidation that the myo-inositol moiety in the intact triphosphoinositide is substituted on the 1, 4, and 5 or 6 hydrosyl groups. When the phospholipid was hydrolyzed in base, several polyphosphate esters of myo-inositol were obtained (2). The mixture contained two triphosphates, two diphosphates, and one monophosphate. The major triphosphate ester was established as being L-myo-inositol 1,4,5 (or 6)triphosphate, whereas it was shown that one of the diphosphates was either n-myo-inositol 4,5or 1 , 6-diphosphate. The monophosphate was identical in properties, with the exception of the infrared spectrum, with synthetic nn-myo-inositol 4-phosphate. Since it was optically active, the conclusion was that it must be one of the pure optical isomers of myo-inositol4-phosphate. We have also pointed out the interesting fact that the absolute configuration of the n-myo-inositol 1,4,5(6) triphosphate is the same as that found for soybean monophosphoinositide (4, 5) and more recently for a monophosphoinositide from horse liver 03. This paper presents further studies on the structures of the myo-inositol phosphate components from the brain phosphoinositide, and describes their complete characterization. The partially characterized diand triphosphate esters obtained by base hydrolysis of the brain phosphoinositide now have been shown to be L-myo-inositol 4,5-diphosphate and L-myo-inositol 1,4,5triphosphate. The two components whose structures were not elaborated in the earlier reports are shown to be myoinositol 1,4-diphosphate and myo-inositol 2,4,5-triphosphate. The close structural relationships of all of these compounds suggest an interrelated biochemical role.