Myo-inositol phosphates obtained by alkaline hydrolysis of beef brain phosphoinositide.

It is now apparent that the nutritional requirement for myoinositol in many cells is related to its participation as a building unit of myo-inositol-containing phospholipids (phosphoinositides). This explains why Eastcott (1)) in her classic work, found that all the myo-inositol taken up from the medium by growing yeast could be recovered by acid hydrolysis of the cells. The role of phosphoinositides in cellular metabolism has not been defined. However, experiments described recently, in which the metabolic turnover of phosphoinositides was enhanced in pigeon pancreas which was treated with acetylcholine to stimulate protein excretion, led to the suggestion that these phospholipids might be involved “in the active t.ransport of certain types of molecules” (2). Although such speculation about the biological function of phosphoinositides is engaging attention, precise knowledge as to the structures of these compounds would make the speculation more fruitful. Careful chemical studies during the last 10 years on the simplest of the phosphoinositides have established that this substance is adequately described as a phosphatidyl myoinositol (3). The remaining question about its structure pertained to the position of the linkage to the myo-inositol ring. We have recently established that the phosphatidyl group is attached in one of the enantiomorphic l-positions of myo-inositol (4), that the myo-inositol therefore becomes asymmetric by substitution in much the same way as does glycerol in n-glycerol 3phosphate, and that the compound from soybean may be called I-phosphatidyl-n-myo-inositol (5). Similar, if not identical, “monophosphoinositides” occur in many plant and animal tissues, and in all examples so far investigated the position of substitution on the myo-inositol ring is the same.