732. Phospholipids. Part VII. The structure of a monophosphoinositide

Abstract

The monophosphoinositide isolated from horse liver has been shown to beThe nature of the 2,3-di-O-acyl-~-glycerol l-(L-myoinositol l-phosphate) .long-chain fatty acids has not been investigated.PAPERS in this series have described studies on a variety of phosphate esters with the object of extending knowledge of the chemistry and structure of phospholipids, particularly those containing inositol. Phosphoinositides are very widely distributed.2 The lipid from horse liver was chosen for an initial application of the degradative methods previously examined on model substances, as it was reported to be present in relatively high concentration (-0.2y0).495 A brieE account of part of our work on this inositide has already been published.6 isolated a phosphoinositide, almost nitrogen-free, from horse liver and showed that on hydrolysis it gave myoinositol, glycerol, fatty acids, and orthophosphate in the ratio 1 : 1 : 2 : 1. I t was a secondary phosphate and gave myoinositol phosphate on alkaline hydrolysis. In the present work the liver phospholipids were extracted by a modification of a method due to Folch et aZ.8 and the pure monophosphoinositide was separated by chromatography on silicic acid with the elution procedure of Hanahan and his co-w~rkers.~*~ The product was a colourless, amorphous sodium salt with analytical values corresponding to those of a diacylglycerol inositol phosphate,* the structure suggested by McKibbin.' The substance is shown to have the structure (I; R = acyl), in which the stereochemistry is completely defined. The composition of the fatty acid mixture obtained on hydrolysis has not been studied.Hydrolysis by acetic l1 or hydrochloric acid, applied variously to the inositides from wheat germ, cardiac muscle, beef and rat liver, and yeast, leads to diglyceride. The reaction is undoubtedly dependent l2 on an acid-catalysed displacement of the diglyceride residue by the neighbouring hydroxyl group on the myoinositol. Applied to the horseliver lipid, hydrolysis by acetic acid led to diglyceride and myoinositol phosphates ; neither monoglyceride nor glycerol phosphate was detected. Thus both fatty acids are esterified to the glycerol residue. This was confirmed by treating the phospholipid with periodate: the inositol residue was destroyed and a product indistinguishable chromatographically from a synthetic phosphatidic acid (11; R = acyl) was formed. This substance, without isolation, was hydrolysed by alkali which removed the fatty acids, to yield a glycerol phosphate isolated as its cyclohexylamine salt. Periodate oxidation and chromatographic comparisons showed it to be the l-phosphate, uncontaminated by the 2-isomer. Muscle glycerophosphate-dehydrogenase has been shown l3 to be specific for the D-1 C , , acids.1° McKibbin* Calculated as the distearate. Liver phosphoinositides appear to contain a high proportion of 1

Phosphoglycopeptide, a major constituent of the spermatophoric plasma of the octopus (Octopus dofleini martini)

“…(Dawson, Hemington & Davenport, 1962); (e) isopropanol:water:NH3 (7:2:1 by vol.) (Brown, Clark & Letters, 1961); (f) 77% ethanol (Block et al, 1958). In some instances electrophoresis in system (a) was carried out before the chromatography of neutral sugars in order to remove interfering ions.…”

Glyceride isomerizations in lipid chemistry

“…11) would be extremely unstable because of high ring strain and would be quickly converted to a more stable intermediate (III) with an exo-double bond on the ring. The cyclic phosphates have been prepared and identified (70,71,80,81). The cyclic phosphates have been prepared and identified (70,71,80,81).…”

A short history of inositol lipids

“…In the modern context of signaling, Ballou's contributions to the structures of polyphosphoinositol lipids (discussed below) are the best known, but the extensive body of earlier work that included de novo synthesis of new enantiomers to establish PI's structure (25) was an equally important and elegant piece of work. Parallel work by Dan Brown and his colleagues (26) made an additional crucial contribution to the establishment of PI structure.…”