Cycloartanes from the red alga Galaxaura sp.
Six cycloartane triterpenes have been isolated from the red alga Galaxaura sp. The new structures (galaxaurols A–E) were determined to be methyl 3β-hydroxy-23-oxocycloart-24-en-29-oate (2), methyl 23(E)-3β-hydroxy-25-methoxycycloart-23-en-29-oate (3), methyl 23(E)-3β-hydroxycycloarta-23,25-dien-29-oate (4), 23(E)-25-methoxycycloart-23-en-3β,29-diol (5), and cycloart-24-en-3β,23α,29-triol (6), respectively.
Dissecting the sterol C-4 demethylation process in higher plants. From structures and genes to catalytic mechanism
Sterols become functional only after removal of the two methyl groups at C-4. This review focuses on the sterol C-4 demethylation process in higher plants. An intriguing aspect in the removal of the two C-4 methyl groups of sterol precursors in plants is that it does not occur consecutively as it does in yeast and animals, but is interrupted by several enzymatic steps. Each C-4 demethylation step involves the sequential participation of three individual enzymatic reactions including a sterol methyl oxidase (SMO), a 3β-hydroxysteroid-dehydrogenase/C4-decarboxylase (3βHSD/D) and a 3-ketosteroid reductase (SR). The distant location of the two C-4 demethylations in the sterol pathway requires distinct SMOs with respective substrate specificity. Combination of genetic and molecular enzymological approaches allowed a thorough identification and functional characterization of two distinct families of SMOs genes and two 3βHSD/D genes. For the latter, these studies provided the first molecularly and functionally characterized HSDs from a short chain dehydrogenase/reductase family in plants, and the first data on 3-D molecular interactions of an enzyme of the postoxidosqualene cyclase sterol biosynthetic pathway with its substrate in animals, yeast and higher plants. Characterization of these three new components involved in C-4 demethylation participates to the completion of the molecular inventory of sterol synthesis in higher plants.
Application of Carbowax 20M as an open-tubular liquid phase in analyses of nutritionally important fats and oils.
In the first part, the reasons for the choice of Carbowax 20M-terephthalic acid as a liquid phase are indicated and the technique for preparation of columns is descirbed. The ECL of 14 to 24 carbon fatty acids (branched and positional isomers of unsaturated acids) as well as the accuracy of determination of some fatty acids, are presented. In the second part, examples of chromatograms are given as well as tables concerning the composition of various fats: vegetable oils, depot fats, and fats from organs of monogastric species, polygastric species, and fish.