Acylated Steryl Glycosides Research Articles

Enzymatic acylation of steryl glycoside

Summary A soluble protein fraction obtained from leaves of Vicia faba catalyzes the acylation of steryl glycoside to acyl steryl glycoside by acyl groups originating from galactolipids. Using semisynthetic alactolipids it was shown that both acyl groups from C-1 and C-2 of mono- and digalactosyl diglyceride are transferred to steryl glycoside. The same protein fraction was also active in the formation of acyl galactosyl diglyceride. Using the same semisynthetic galactolipids as above it was demonstrated by mass spectrometry that during formation of acyl galactosyl diglyceride the acyl groups from the donor molecules are transferred exclusively to the galactose moiety of the accepting monogalactosyl diglyceride, its diglyceride portion remaining unaltered. After working out an assay based on the transfer of tritiated oleoyl groups from digalactosyl diglyceride to steryl glycoside it was shown that most of the soluble activity in leaf homogenates was not localized in chloroplasts.

Phytosterols in tobacco leaves at various stages of physiological maturity

Leaves of varying maturity from 84-day-old tobacco plants were harvested and analyzed for total sterol and their individual sterol components. The mature leaves had a significant higher sterol content than the immature leaves. Separation into free sterols, steryl esters, steryl glycosides, and acylated steryl glycosides showed that the free sterols accounted for most of the sterol increase, and stimgasterol was principally responsible for this increase.

Sterol Accumulation and Composition in Developing Zea mays L. Kernels

Kernels were collected from three maize (Zea mays L.) inbreds from 10 days after pollination until kernel maturity. Sitosterol, campesterol, and stigmasterol were the major sterols at all stages of kernel development. Cholesterol was less than 1% of the dry weight. The three major sterols accumulated during kernel development, but at a rate slower than dry weight. The ratio of the sterols did not vary greatly among the inbreds. At maturity, the three inbreds, Wf9, Oh43, and Ky226, had sterol levels of 325, 228, and 173 micrograms per kernel, respectively. Sitosterol accounted for 75 to 85% of the sterol. The relative amount of stigmasterol decreased during the linear phase of development, while sitosterol increased in the free fraction and campesterol increased in the steryl ester fraction.Free sterols and steryl esters were the major sterol fractions and steryl glycosides and acylated steryl glycosides were only minor components during kernel development. Free sterol content decreased rapidly in two maize inbreds between 10 and 26 days after pollination, but partially recovered in one of the inbreds during final stages of development. In the same two inbreds the steryl ester content reached a maximum during the late stages of linear kernel growth.

Steryl Glycoside Formation in Seedlings of Nicotiana tabacum L.

Particulate enzyme preparations from tobacco seedlings (Nicotiana tabacum L.) were used in the synthesis of steryl glycoside. The data obtained by measuring cholesterol-4-(14)C incorporation generally agree with results obtained with UDP-glucose-(14)C. The in vitro reaction was linear for the first 10 minutes and had a pH optimum of 7.0 to 7.4. Addition of ATP activated while UDP-glucose inhibited slightly the reaction. In short term experiments, the percentage disappearance of endogenous and added sterol was about the same.Intact tobacco seedlings incorporated cholesterol-4-(14)C and sitosterol-4-(14)C into their steryl glycosides. The acylated steryl glycosides were more rapidly labeled than the nonacylated form. After 12 hours of incubation with cholesterol-4-(14)C, about 5% of the radioactivity was recovered as steryl glycoside and 12% as acylated steryl glycoside. Incubation for 12 hours with authentic cholesteryl-(14)C glucoside gave only a 4% acylation, and under these conditions 21% of the radioactivity was recovered as free cholesterol. It is suggested that acylated steryl glycosides may be formed through the acylation of steryl glycosides or the transfer of an acyl-glycosyl group to sterol.

Sterol Changes during Germination of Nicotiana tabacum Seeds

The identity, composition, and concentration of the total, free, esterified, and glycosidic sterol fractions were determined during germination of tobacco seeds. The total, free, and esterified sterols increased, with stigmasterol and campesterol accounting for most of the increase. Steryl glycosides decreased during germination, and stigmasteryl and sitosteryl glycosides showed the largest decrease. During germination, sitosterol was the major sterol in all fractions but stigmasterol and campesterol showed the greatest changes. The fatty acid composition of the steryl esters and acylated steryl glycosides most closely resembled the di- and triglycerides.

Fettsäuremuster im pflanzlichen Acyl-Steringlycosid

Fatty acids of acyl steryl glycoside (acyl SG) of different plants producing both green and photosynthetically inactive tissue have been analyzed. The major components are in all cases 16:0, 18:2 and 18:3 acids. The fatty acid composition of acyl SG of green parts is very similar to that of etiolated, pale or storage tissue of the same plant. Generally the degree of saturation of acyl SG is higher than that of the corresponding total lipid. Acyl SG tends to be more saturated in green parts than in colorless tissues of the same plant. Conversely, total lipid of green tissue containing large amounts of galactolipids and 18:3 acid is much less saturated than that of photosynthetically inactive tissue. Though containing smaller amounts of 18:3, and in some cases unsaturated C 16 acids, acyl SG does not reflect the drastic increase of these acids in the total lipid of green tissue. It is concluded that fatty acids of acyl SG originate mainly from an acyl donor other than chloroplast galactolipids.

Inhibition of Glycolipid Biosynthesis in Chloroplasts by Ozone and Sulfhydryl Reagents

The metabolism of uridine 5'-pyrophosphate-galactose by spinach (Spinacia oleracea) chloroplast preparations was inhibited by ozone. The formation of digalactosyl diglyceride and trigalactosyl diglyceride was inhibited much more than the formation of monogalactosyl diglyceride, steryl glycoside, and acylated steryl glycoside. Essentially identical results were obtained when glycolipid synthesis was inhibited by N-ethyl maleimide, p-hydroxymercuribenzoate, and CdCl(2). Iodoacetate and iodoacetamide affected neither the total incorporation of sugar from uridine 5'-pyrophosphate-galactose nor distribution of the incorporated sugar in the various glycolipids.Ozone reacted with model membrane systems prepared with egg lecithin. In the absence of reduced glutathione, products included malonaldehyde and hydrogen peroxide. In the presence of glutathione, malonaldehyde was still produced, but the glutathione was oxidized and no peroxide was detected. When these studies were extended to chloroplast preparations, it was also found that malonaldehyde was produced and glutathione was oxidized.It was concluded that ozone inhibits glycolipid biosynthesis in chloroplast preparations by way of oxidation of enzyme sulfhydryl groups but that this reaction may be a secondary effect of oxidation of unsaturated fatty acids.