Biosynthesis and interconversion of sterols in plants and marine invertebrates

Comparison of the chromatographic properties of sterols, select additional steroids and triterpenoids: gravity-flow column liquid chromatography, thin-layer chromatography, gas-liquid chromatography and high-performance liquid chromatography

The chromatographic properties of approximately 100 sterols, select steroids of plant origin (sapogenins and steroidal alkaloids) and triterpenoids has been evaluated in this laboratory by monitoring their elution characteristics in adsorption (gravity column and thin-layer methods with and without the addition of silver nitrates), gas and reversed-phase high-performance liquid chromatography. The utility of each methodology to act in one or another chromatographic mode-separation, radio-chemical purification, quantitation and structural elucidation, is discussed. The importance of the tilt of the -OH group at C-3 as well as the polarity, size, an shape of the rest of the molecule as it effects the hydrogen-bonding ability of the -OH group is demonstrated through changes in chromatographic behavior that result from the step-wise introduction of double bonds, methyl, bromo, oxygen, nitrogen and cyclopropyl groups into 5 alpha-cholestanol. An independent aid in the structure identification and quantitation of the compounds was use of a multiple-wavelength diode array detector in which different wavelengths of the UV spectrum (200-400 nm) were simultaneously monitored following passage of the sample through a reversed-phase C18 column.

Paclobutrazol inhibition of sterol biosynthesis in a cell suspension culture and evidence of an essential role for 24-ethylsterol in plant cell division

Growth of a celery (Apium gravidens) cell suspension culture was inhibited by the synthetic plant growth regulator paclobutrazol. Paclobutrazol caused a reduction in the incorporation of [2-14C]acetate into the 4-demethyl sterols (campesterol, sitosterol, stigmasterol) but radioactivity accumulated in the 4 alpha-methylsterols. The accumulating 4 alpha-methylsterols were identified as obtusifoliol and cycloeucalenol indicating that paclobutrazol was inhibiting sterol biosynthesis by blocking 14 alpha-demethylation. The inhibition of celery cell growth by paclobutrazol could be partially overcome by addition of cholesterol to the culture medium. However, addition of stigmasterol restored growth to the control value suggesting an essential role for a 24-ethylsterol to support plant cell division.

Strategy for the analysis of steryl esters from plant and animal tissues

Methods are described for the analysis of intact steryl esters present in complex mixtures isolated from plant or animal tissues. A preliminary examination by analytical thin-layer chromatography (TLC) and capillary column gas chromatography-mass spectrometry (GC-MS) under electron impact (EI) ionisation reveals the complexity of the mixture and the nature of the steryl moieties. Preparative TLC is then utilised to separate the steryl esters into two broad groups, containing fatty acyl moieties of shorter (C2-C8) or longer chain length (C10-C22). The shorter-chain fatty acyl steryl esters are separated by adsorption high-performance liquid chromatography (HPLC) on a LiChrosorb Silica-60 column. The steryl esters with longer-chain fatty acyl moieties are analysed by reversed-phase HPLC on either an Ultrasphere ODS, 5-micron, or a S3 Spherisorb ODS, 3-micron, column. Steryl esters with unsaturated fatty acyl moieties are eluted with the shorter-chain fatty acyl steryl esters. The presence of the unsaturated fatty acyl esters can be monitored by analytical argentation TLC, which will also reveal the degree of unsaturation. The steryl esters are fractionated into the saturated, mono-, di-, tri- and polyene acyl types by preparative medium-pressure liquid chromatography on a column of 10% AgNO3-silica gel. Each of these steryl ester types can then be resubmitted to reversed-phase HPLC or analysed by GC-MS on a short fused-silica capillary column with a bonded phase of the OV-1 type. GC-MS on a magnetic-sector instrument under negative-ion chemical ionisation conditions with ammonia as the reagent gas produces fragment ions for both the steryl and fatty acyl moieties, thus permitting identification of the individual intact steryl esters. These various methods are illustrated by analyses of the steryl ester mixtures obtained from human plasma, barley seedlings, palm oil and rape seed oil.