Previous work from this laboratory has shown that a derivative of [3H]mevalonic acid is incorporated into a number of specific proteins in Halobacterium halobium and Halobacterium cutirubrum and that the major radioactive material released by treatment with methyl iodide was neither farnesyl nor geranylgeranyl compound, which have been generally accepted to be prenyl groups of a number of prenylated proteins found in eukaryotic cells, but an unknown compound (Sagami, H., Kikuchi, A., and Ogura, K. (1994) Biochem. Biophys. Res. Commun. 203, 972-978). In the current study, the unknown compound was prepared in a large amount from H. halobium cells and analyzed by reverse and normal phase high performance liquid chromatographies followed by mass spectrometry. The mass spectrum of this compound exhibited a parent ion peak (M+) at m/z 682, suggesting that it is a 1-methylthio-2,3-di-Ο-(3′,7′,11′,15′- tetramethylhexadecyl)glycerol (diphytanylglyceryl methylthioether). Diphytanylglyceryl methyl thioether was chemically synthesized, and its mass fragmentation pattern was completely coincident with that of the mevalonic acid-derived material from H. halobium. These results indicate that Halobacteria contains specific proteins with a novel type of modification of a cysteine residue of the proteins with a diphytanylglyceryl group in thioether linkage.
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