Isolation and characterization of Zymomonas mobilis mutants resistant to octadecyltrimethylammonium chloride,a detergent acting on hopanoid-producing bacteria

Growth of the hopanoid-producing bacterium Zymomonas mobilis was inhibited at low concentrations of the cationic detergent octadecyltrimethylammoniumchloride (OTAC). A relationship between sensitivity of Zymomonas mobilis to OTAC, presence of hopanoids and ethanol tolerance was postulated. Mutants resistant to OTAC were isolated from strains ZM1 and ZM4. They did not present any alteration of the hopanoid content and their squalene cyclases showed the same sensitity to OTAC as the parent enzymes. Resistance to OTAC paralleled pleiotropic effects including, enhanced accessibility of the membrane-bound alkaline phosphatase, important release of proteins from cells by Tris/HCl treatment, increased resistance to antibiotics and increased sensitivity to ethanol. In addition, OTAC^R mutants were also characterized by the synthesis or the overproduction of an outer membrane protein (F53) not detected on 2D-PAGE maps of parent strains and by a normal heat shock response. The role of hopanoids, heat shock proteins, protein F53 and membrane organization in ethanol tolerance is discussed.Abbreviations OTAC octadecyltrimethylammoniumchloride - SLS sodium lauryl sarcosinate     

Peroxisomes and peroxisomal enzymes along the crypt-villus axis of the rat intestine

Abstract. The development of peroxisomes and expression of their enzymes were investigated in differentiating intestinal epithelial cells during their migration along the crypt-villus axis. Sequential cell populations harvested by a low-temperature method were identified by microscopy, determination of alkaline phosphatase and sucrase activities and incorporation of [³H]-thymidine into DNA. Ultrastructural cytochemistry after staining for catalase activity, revealed the presence of peroxisomes in undifferentiated stem cells located in the crypt region. Morphometry indicated that the number of these organelles increased as intestinal epithelial cells differentiate. Catalase activity was higher in the crypt cells than in the mature enterocytes harvested from villus tips. On the other hand, an increasing gradient of activity was observed from crypts to villus tips for peroxisomal oxidases, i.e. fatty acyl coA oxidase, D-amino acid oxidase and polyamine oxidase. These findings indicate that biogenesis of peroxisomes occurs during migration of intestinal epithelial cells along the crypt-villus axis and that peroxisomal oxidases contribute substantially to the biochemical maturation of enterocytes.     

Étude thermodynamique de la transition hélice–pelote statistique en solvants mixtes de différents esters de l'acide poly(L-glutamique)

Helix–coil transition of poly(γ-methyl-L -glutamate), poly(γ-ethyl-L -glutamate), and poly(γ-benzyl-L -glutamate) has been studied in mixed solvents by calorimetry, polarimetry, and viscometry. The experimental data have allowed the evaluation of solvation enthalpy Δh_b, equilibrium constant K for hydrogen bond formation between the active solvent component and CO and NH groups, and the cooperativity parameter σ. The conformational transition of polypeptides in solution in a mixed solvent containing enough active solvent to maintain the coiled conformation has been produced by dilution with the helix-supporting solvent for the measurements of enthalpy of transition Δh_s. The average value for Δh_s is 3550 ± 300 J/mol and is practically independent of the nature of the side chain for the dichloroacetic acid-ethylene dichloride solvent pair at 25°C. A noticeable concentration effect exists in the case of poly(γ-benzyl-L -glutamate). The helical conformation is less stable for poly(γ-ethyl-L -glutamate), and this is explained by a steric effect hindering the access of dichloroacetic acid to side chains. Constant K has been calculated using polarimetric data and also from values of Δh_s obtained at different temperatures using the Bixon and Lifson theory on the one hand and that of Sayama and coworkers on the other hand. Values of σ for poly(γ-ethyl-L -glutamate) have been calculated according to both theories mentioned, and the results show that the two sets of values are quite similar. The constant σ depends on the nature of the active solvent, on temperature, and on the binary-solvent composition. These conclusions are confirmed by viscometric results. Values of Δh_b calculated from constant K are 5230 J/mol when Bixon and Lifson theory is used and 5569 J/mol when the theory at Sayama and coworkers is used. In both cases the value for Δh_b is much lower than that of an intramolecular hydrogen bond. Experimental results suggest that the solvation mechanism would proceed in a manner so that mechanisms described in both theories are involved.     

Influence of thyroid status on the electrophoretic pattern of rat liver mitochondrial proteins]

Liver mitochondria were isolated from normal and thyroidectomized rats and their protein components analyzed by polyacrylamide gel electrophoresis. In whole mitochondria 35 protein fractions with MW ranging from 10,000 to 135,000 were characterized. In the absence of thyroid hormone secretion, the amount of a MW 54,000 fraction was always decreased. Injection of small doses of 3,5,3'-triiodo-L-thyronine to the thyroidectomized animal restored the quantity of that protein fraction to normal. Isolated outer mitochondrial membranes showed the presence of 20 protein fractions. These fractions revealed no change after thyroidectomy. The mitoplast, which contained 35 fractions, exhibited a decrease of the MW 54,000 component in thyroidectomized rats. The mitoplast was separated into several fractions. Water soluble matrix proteins presented molecular weights ranging between 40,000 and 55,000. Proteins, which were slightly bound to the inner mitochondrial membrane and could be extracted by KCl, presented molecular weights between 25,000 and 45,000. Structural proteins showed a principal specific component of MW equals 23,000. Electrophoretic patterns obtained with these submitochondrial fractions were similar in normal and thyroidectomized animals. The mitoplast fraction which contained the insoluble cytochromes (a, a3, b, c1) was isolated ; its principal constituent, of MW 54,000 was significantly decreased after thyroidectomy. Thus, the lack of thyroid hormone secretion lowered the level of a protein constituent bound to the inner membrane of liver mitochondria. The synthesis of this constituent could be controlled by mitochondrial nucleic acids.