SUMMARY: Inner and outer membranes were isolated from by sucrose density centrifugation after disruption of bacteria by shaking with glass beads. The outer membrane (OM) contained all the pink oxocarotenoid pigment of the cell and unusually small amounts of phospholipid and lipopolysaccharide. An unidentified glucan was present in both membrane fractions. Several major OM proteins had molecular sizes in the range 49 kDa to 80 kDa and most of the OM proteins remained insoluble when OM or cell wall was treated with 2% (w/v) sodium dodecyl sulphate (SDS) at temperatures up to 50°C. Neither polysaccharide nor phospholipid was solubilized under the same conditions. Increasing the concentration of methanol in the growth medium led to an increase in the bacterial phospholipid content and to increased solubility of the OM in 2% SDS. It is suggested that the resistance of the OM to solubilization by the detergent is due in part to the presence of large amounts of three unidentified polar, phosphate-free lipids that might be related to hopane polyols. Phospholipids in isolated walls and OM were rapidly degraded by endogenous phospholipase when incubated in Tris buffer at pH 8 but the unidentified lipids were retained in the particulate fraction.


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