The effect of chylomicron remnants on bile acid synthesis in cultured rat hepatocytes

The effect of chylomicron remnants on bile acid synthesis in isolated rat hepatocytes in monolayer cultures was investigated. Production of bile acids by the cells in the presence of chylomicron remnants at a cholesterol concentration of 7.8-9 nmol/ml was increased by approx. 75% after 17 h and 25% after 24 h incubation. Similar concentrations of cholesterol added to the cells in the form of chylomicrons had no significant effect on bile acid synthesis. These results suggest that cholesterol taken up in chylomicron remnants may be an important source of substrate for bile acid synthesis.     

The effect of inhibition of cholesterol esterification on the fate of cholesterol derived from HDL in rat hepatocyte monolayers

Rat HDL2 is known to stimulate bile acid synthesis in rat hepatocyte monolayers. The intracellular fate of the cholesterol derived from the HDL2 was studied using the inhibitor of cholesterol esterification, Sandoz compound 58-035. Rat HDL2 added to rat hepatocyte monolayers caused a stimulation of cholesterol esterification of 32%. This stimulation could be inhibited by 58-035. A small significant increase in bile acid synthesis was also observed in cells in the presence of HDL2, confirming our earlier observations. 58-035 prevented this increase. These observations imply that cholesterol entering the cell from HDL2 is first esterified and can only enter the substrate pool for bile acid synthesis after subsequent intracellular hydrolysis.     

Phylogeny of Greya (Lepidoptera: Prodoxidae), based on nucleotide sequence variation in mitochondrial cytochrome oxidase I and II: congruence with morphological data

The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from nucleotide sequence variation across a 765-bp region in the cytochrome oxidase I and II genes of the mitochondrial genome. Most parsimonious relationships of 25 haplotypes from 16 Greya species and two outgroup genera (Tetragma and Prodoxus) showed substantial congruence with the species relationships indicated by morphological variation. Differences between mitochondrial and morphological trees were found primarily in the positions of two species, G. variabilis and G. pectinifera, and in the branching order of the three major species groups in the genus. Conflicts between the data sets were examined by comparing levels of homoplasy in characters supporting alternative hypotheses. The phylogeny of Greya species suggests that host-plant association at the family level and larval feeding mode are conservative characters. Transition/transversion ratios estimated by reconstruction of nucleotide substitutions on the phylogeny had a range of 2.0-9.3, when different subsets of the phylogeny were used. The decline of this ratio with the increase in maximum sequence divergence among taxa indicates that transitions are masked by transversions along deeper internodes or long branches of the phylogeny. Among transitions, substitutions of A-->G and T-->C outnumbered their reciprocal substitutions by 2-6 times, presumably because of the approximately 4:1 (77%) A+T-bias in nucleotide base composition. Of all transversions, 73%-80% were A<-->T substitutions, 85% of which occurred at third positions of codons; these estimates did not decrease with an increase in maximum sequence divergence of taxa included in the analysis. The high frequency of A<-->T substitutions is either a reflection or an explanation of the 92% A+T bias at third codon positions.      

Solvent effects on biocatalysis in organic systems: equilibrium position and rates of lipase catalyzed esterification

Porcine pancreatic lipase immobilized on celite particles has been employed as a catalyst for the esterification of dodecanol and decanoic acid in a predominantly organic system. Solvent influence on the equilibrium position and on the catalyst activity has been studied using 20 solvents, including aliphatic and aromatic hydrocarbons, ethers, ketones, nitro- and halogenated hydrocarbons, and esters. The equilibrium constant for esterification correlates well with the solubility of water in the organic solvent, which in turn shows a good relationship with a function of Guttman's donor number and the electron pair acceptance index number of the solvent. This may be rationalized in terms of the requirements for solvation of water and of the reactants. The catalyst activity, measured as the initial rate of the esterification reaction, is best correlated as a function of both n-octanol-water partition coefficient (log P) and either the electron pair acceptance index or the polarizability.