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Purified phosphatidylinositol-specific phospholipase C from Staphylococcus aureus released a substantial proportion of the total alkaline phosphatase activity from a wide range of tissues from several mammalian species. Co-purification of the phospholipase C and alkaline phosphatase-releasing activities and the inhibition of both these activities by iso-osmotic salt solutions suggested that the releasing effect was unlikely to be due to a contaminant.

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The myelin sheath of nerve fibers represents one of the most highly organized components of biological systems, which, despite its marked lability, has proved to be uniquely suitable for a systematic analysis by combined application of physical and chemical techniques. Extensive polarized light studies (4,34,(48)(49)(50)(51) of the strong birefringence of the sheath suggested it to be built up of concentrically disposed protein lamellae alternating with submicroscopic layers of lipide molecules oriented with their long axes in the radial direction. Low-angle x-ray diffraction studies (1, 5-7, 21-32, 51-55) supported this concept and furnished quantitative data on the highly ordered arrangement of the lipide, protein, and water components in the normal myelin structure. The fundamental x-ray diffraction spacings of 170 A found in amphibian and of 180 to 185 A in mammalian nerves were assumed to correspond to the thickness of the concentric lipide-protein layers deduced from polarized light investigations.The postulated layers and their exceptionally regular concentric arrangement in the myelin sheath were subsequently observed directly in the electron microscope (8-20, 35). However, this remarkable demonstration of structural regularity at the macromolecular level achieved by direct and indirect methods is still inadequate if it cannot be referred to the specific localization of chemical components in the sheath. Thus, the concentric laminated structure observed in electron micrographs of thin nerve sections is simply a pattern of the selective deposition of osmium at certain sites, and cannot as yet be interpreted in terms of specific regions containing lipides, lipoproteins, or protein constitutents. Likewise, the low angle x-ray diffraction patterns recorded from normal nerve can only furnish general information on the dimensions and approximate distribution of scattering groups in the radial direction of the sheath. Further attempts to correlate these structural parameters with the chemical composition of the sheath are thwarted by our lack of knowledge of the chemical nature and * Permanent address:

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