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Caenorhabditis elegans was cultured in semi-defined medium containing yeast extract, soy peptone, glucose, hemoglobin, Tween 80, and sitosterol. Monoglycosylceramides were chromatographically purified from nematode extracts. Their structures were elucidated with mass spectrometry, nuclear magnetic resonance spectroscopy, and analysis of methanolysis products of the parent cerebrosides. The glycosylceramides were unusual in that the only long-chain sphingoid base detected was an iso-branched compound with a C-4 double bond (i.e., 15-methyl-2-aminohexadec-4-en-1,3-diol). Glucose was the only sugar moiety detected. The fatty acids consisted of a series of primarily straight-chain, saturated, 2-hydroxylated C20-C26 acids; some iso-branched analogs also occurred. The sphingomyelins of C. elegans were also hydrolyzed, and the same iso-branched C17 compound was the only sphingoid base detected. This is the first structural analysis of a nematode glycosphingolipid and the first report of an organism in which the long-chain sphingoid bases are entirely iso-branched.

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The first protonation site of [Vlo02,]6differs both from the second protonation site and from the site of preferential interaction with aqueous manganese(i1) ion. It is probably an out-of-plane apex, and not a bridging oxygen as has recently been proposed. The 61V n.m.r. linewidths are almost independent of direct protonation but depend in-Coventry CV4 7AL directly on more distant protonation. THE isopolyvanadate ion [Vl,02,]6-has the structure shown in Figure 1 in all the crystals in which it has so far Q f FIGURE 1 Crystal structure of [Vl0O2.J6-(refs. 1 and 2)been identified.1.2 Recently, high-field 51V n.m.r. studies 3 9 4 have greatly improved upon early derivativemode n.m.r. studies5'6 and have confirmed that the 4 : 4 : 2 population ratio of three distinct vanadium-atom types, present in the solid, also persists in solution. However, the pH dependence of these resonances has not yet been studied in any detail. Conventional pH studies of this system ' 9 , have not been easy because of its metastability and sensitivity to ionic strength and counter ion. However, they show successive pKa values in the ranges pK, 5.5-6.0, pK2 3.1-3.7, and pK3 z 2. At pH < 2 the ion hydrolyses fairly rapidly to give [V02(OH2),]+,g and at pH < 6.5 it hydrolyses slowly to give various tetrahedral specie^.^^^^ Vanadium41 n.m.r. spectra should give additional information about the separate protonation sites, and should be less sensitive than conventional pH studies to the system's metastability.Polyoxoanions are generally believed to protonate at terminal oxygens, and therefore some workers have

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