Carotenoids acts as reinforcers of the Acholeplasma laidlawii lipid bilayer.

Acholeplasma laidlawii cells grown with oleic acid produced much more colored carotenoids than did cells grown with elaidic acid. The amount of carotenoids was decreased 80 to 90% by growing the cells with 0.05 M propionate, resulting in a marked increase in the mobility of both 5-doxylstearate and 12-doxylstearate incorporated into the membranes. The fatty acid composition of the propionate-grown cells differed from that of cells grown without propionate by containing odd-numbered rather than even-numbered saturated fatty acids, but the ratios of saturated to unsaturated fatty acids were the same. To determine whether the carotenoids are the cause for the restricted mobility in the membranes, the carotenoids were selectively removed from A. laidlawii membranes by incubating the membranes with phosphatidylcholine vesicles. The carotenoid-depleted membranes showed an increase in the mobility of the hydrocarbon chains of the spin-labeled fatty acids. Furthermore, the incorporation of carotenoids into artificial membrane vesicles restricted the mobility of the hydrocarbon chain. Our results support the notion that the carotenoids in A. laidlawii act as a rigid insert reinforcing the membrane bilayer.

Hydantoin immunosuppression and carcinogenesis.

The immunological response of mice submitted to hydantoin treatment was determined. Hydantoin reduced the absolute number of spleen cells in treated animals and did not modify spleen cells reactivity to concanavalin A, although the response to SRBC challenge, as measured by the Jerne plaque-forming cell technique, was significantly decreased. Following these findings, the influence of hydantoin on carcinogenesis was evaluated by using the model of urethane-induced lung adenomas in SWR mice. Treatment with hydantoin significantly reduced the incidence of the induced adenomas. We confirmed that hydantoin modifies the immune response of the host mainly by depressing its humoral function and we have shown that this effect was associated with an inhibitory effect on tumour induction.

Thermal regulation of the fatty acid composition of lipopolysaccharides and phospholipids of Proteus mirabilis.

The fatty acid composition of the lipid A moiety of the lipopolysaccharide and phospholipid fractions of Proteus mirabilis changed significantly on varying the growth temperature. A decrease in the growth temperature from 43 degrees C to 15 degrees C resulted in a decrease in the palmitic acid content of the lipopolysaccharide from 19.4% of total fatty acids at 43 degrees C to 1.4% at 15 degrees C, and by the appearance of an unsaturated fatty acid residue, hexadecenoic acid. Changes in the 3-hydroxy-myristic acid content of the lipid A were minimal. The decrease in the growth temperature also resulted in a decrease in the saturated fatty acid content of the phospholipid fraction, which was accompanied by an increase in their fluidity, as measured by the freedom of motion of spin-labeled fatty acids incorporated into dispersions made of the phospholipids. Nevertheless, the fluidity obtained with membrane phospholipids extracted from the cells grown at various temperatures were essentially the same when fluidity was determined at the growth temperature, supporting the hypothesis that variations in the fatty acid composition of membrane phospholipids serve to produce membranes having a constant fluidity at different temperatures of growth.

Cerulenin-induced changes in the lipopolysaccharide content and phospholipid composition of Proteus mirabilis.

Inhibition of Proteus mirabilis growth by cerulenin, a specific inhibitor of fatty acid biosynthesis, was reversed by exogenously supplied fatty acid mixtures containing oleic acid and palmitic or pentadecanoic acids. The growth rate of the cells treated with cerulenin in the presence of the fatty acid mixtures was slower, however, than that of untreated cells, and their lipopolysaccharide content was decreased by 30-50%, resulting in an increased sensitivity of the organisms to rifamycin and vancomycin. Polyacrylamide gel electrophoresis of the lipopolysaccharide fraction from cerulenin-treated cells revealed that of the two P. mirabilis lipopolysaccharide types, the relative amount of the higher molecular weight lipopolysaccharide was reduced from 50% to 30% of the total lipopolysaccharide. Fatty acid analysis of the phospholipid and lipopolysaccharide fractions from cells grown with cerulenin, pentadecanoate, and oleate revealed that over 60% of the native even-numbered fatty acids of the phospholipid fraction was substituted by the odd-numbered fatty acid, while no incorporation of either the pentadecanoate or oleate could be demonstrated in the lipid A moiety of the lipopolysaccharide. The only change in the lipid A observed was an increase in the content of 3-hydroxymyristic acid accompanied by a decrease in the nonhydroxylated fatty acids, supporting the highly conserved nature of this molecule.

Outer membrane proteins of smooth and rough strains of Proteus mirabilis.

The outer membranes of the smooth Proteus mirabilis S1959 strain and its rough R13, R110, R51 and R45 mutants were isolated by sonication of the cells and sucrose density gradient centrifugation. The outer membrane of the rough strains had a lower density than that of their parent smooth strain, but the protein-to-phospholipid ratios were the same. The electrophoretic patterns of outer membrane polypeptides of the S and R strains in sodium dodecylsulfate/polyacrylamide gels were identical, with two major polypeptide bands, C1 and C2 (Mr 39,000 and 38,000) predominating. The C1 polypeptide band was a heat-modifiable polypeptide, which migrated as a band at Mr 33,000 when membranes were solubilized at 37 degrees C or 50 degrees C, and at Mr 39,000 when solubilization was at 100 degrees C. Susceptibility of outer membrane polypeptides to proteolytic digestion was found to be higher in isolated outer membrane preparations of the rough strains than in the smooth strain, suggesting that the availability of the polypeptide chains to proteolytic activity depends on the length of the polysaccharide chains of the outer membrane lipopolysaccharide.