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1.
The chemical properties of very low density and high density lipoproteins of adult bullfrog serum were determined. This serum contained extremely low levels of both very low density lipoprotein (10-30 mg/100 ml) and high density lipoprotein (5-10 mg/100 ml). The constituents of very low density lipoprotein, on a weight percentage basis, were found to be 48.1% triglyceride, 17.3% cholesterol ester, 8.8% cholesterol, 11.6% phospholipid, and 12% protein. These constituents were also present in high density lipoprotein with weight percentage values of 3.7%, 19.3%, 11.9%, 25.2%, and 36.8%, respectively. The fatty acid compositions of the triglycerides, cholesterol esters, and phosphatidylcholine were quite similar in the very low density lipoprotein and high density lipoprotein. However, shingomyelin fatty acid composition was appreciably different in the two lipoproteins. Disc gel electrophoresis in sodium dodecyl sulfate-polyacrylamide gels produced patterns with one major (approximate molecular weight, 7,000) and several minor bands for the apoprotein of very low density lipoprotein and one major (approximate molecular weight, 28,000) and several minor bands for that of high density lipoprotein.  相似文献   

2.
In a randomized, cross-over feeding trial involving 10 men with polygenic hypercholesterolemia, a control, Mediterranean-type cholesterol-lowering diet, and a diet of similar composition in which walnuts replaced approximately 35% of energy from unsaturated fat, were given for 6 weeks each. Compared with the control diet, the walnut diet reduced serum total and LDL cholesterol by 4.2% (P = 0.176), and 6.0% (P = 0.087), respectively. No changes were observed in HDL cholesterol, triglycerides, and apolipoprotein A-I levels or in the relative proportion of protein, triglycerides, phospholipids, and cholesteryl esters in LDL particles. The apolipoprotein B level declined in parallel with LDL cholesterol (6.0% reduction). Whole LDL, particularly the triglyceride fraction, was enriched in polyunsaturated fatty acids from walnuts (linoleic and alpha-linolenic acids). In comparison with LDL obtained during the control diet, LDL obtained during the walnut diet showed a 50% increase in association rates to the LDL receptor in human hepatoma HepG2 cells. LDL uptake by HepG2 cells was correlated with alpha-linolenic acid content of the triglyceride plus cholesteryl ester fractions of LDL particles (r(2) = 0.42, P < 0.05). Changes in the quantity and quality of LDL lipid fatty acids after a walnut-enriched diet facilitate receptor-mediated LDL clearance and may contribute to the cholesterol-lowering effect of walnut consumption.  相似文献   

3.
The size of low density lipoproteins (LDL) is strongly correlated with LDL cholesteryl ester (CE) content and coronary artery atherosclerosis in monkeys fed cholesterol and saturated fat. African green monkeys fed 11% (weight) fish oil diets have smaller LDL and less CE per LDL particle than lard-fed animals. We hypothesized that this might be due to a lower plasma lecithin:cholesterol acyltransferase (LCAT) activity in fish oil-fed animals. Using recombinant particles made of egg yolk lecithin-[14C]cholesterol-apoA-I as exogenous substrate, we found no difference in plasma LCAT activity (27 versus 28 nmol CE formed per h/ml) of fish oil- versus lard-fed animals, respectively; furthermore, no diet-induced difference in immunodetectable LCAT was found. However, plasma phospholipids from fish oil-fed animals were over 4-fold enriched in n-3 fatty acids in the sn-2 position compared to those of lard-fed animals. Additionally, the proportion of n-3 fatty acid-containing CE products formed by LCAT, relative to the available n-3 fatty acid in the sn-2 position of phospholipids, was less than one-tenth of that for linoleic acid. The overall rate of LCAT-catalyzed CE formation with phospholipid substrates from fish oil-fed animals was lower (5-50%) than with phospholipid substrates from lard-fed animals. These data show that n-3 fatty acids in phospholipids are not readily utilized by LCAT for formation of CE; rather, LCAT preferentially utilizes linoleic acid for CE formation. The amount of linoleic acid in the sn-2 position of plasma phospholipids is reduced and replaced with n-3 fatty acids in fish oil-fed animals. As a result, LCAT-catalyzed plasma CE formation in vivo is likely reduced in fish oil-fed animals contributing to the decreased cholesteryl ester content and smaller size of LDL particles in the animals of this diet group.  相似文献   

4.
The low-density lipoproteins in pig serum were separated into two subclasses (LDL1 and LDL2) by 2 to 7% pore size gradient gel electrophoresis. Preparative gel electrophoresis in 2 to 4% gradient gel made it possible to isolate these components as distinct entities. After delipidation by chromatography on Sepharose 4B in the presence of SDS, both apo-LDL1 and apo-LDL2 were found to have a molecular weight of 2.6X10(5). However, when these apoproteins were incubated in 10% sodium dodecyl sulfate, fragmentation occurred and the minimum fragment molecular weight was estimated to be 2.4X10(4). No essential difference was found in the amino acid compositions or fragmentation patterns of the apoproteins. However, the amounts of carbohydrates in the two apoproteins were different (7.09% in apo-LDL1 and 5.08% in apo-LDL2). The carbohydrate composition was 0.8% sialic acid, 2.38% N-acetyl-glucosamine, and 4.01% neutral sugars in apo-LDL1 and 0.5, 1.75, and 2.83% in apo-LDL2, respectively. In both apoproteins, mannose, galactose, and fucose were present in almost the same molar ratio of 4-5 : 2-3 : 1.  相似文献   

5.
Lipid composition of Mycoplasma orale was examined and compared with that of horse serum added to the growth medium. Ratios of cholesterol/cholesterol ester and sphingomyelin/phosphatidylcholine were much higher in M. orale than in the horse serum, indicating the organism incorporates selectively cholesterol and sphingomyelin. A distinct difference between the lipids from the two sources was that in phospholipids of M. orale almost all (greater than 95%) of the fatty acyl residues were saturated whereas nearly half of the residues were unsaturated in horse serum phospholipids. Approximately one third of M. orale phospholipids was phosphatidylglycerol, which was synthesized by the organism as was demonstrated by 32P-labeling experiment. Its acyl residues consisted mainly of C16:0 and were efficiently labeled with 14C-palmitate but not with 14C-acetate. These results clearly indicate the de novo synthesis of phosphatidylglycerol by M. orale is through acylation with exogenous saturated fatty acids. On the other hand, all the phosphatidylcholine and sphingomyelin of M. orale were derived from the medium. The 14C-labeling experiment demonstrates that no fatty acid synthesis takes place nor exogenous fatty acid can be incorporated so efficiently as phosphatidylglycerol, suggesting that extremely high proportion of saturated fatty acyl residues in these phospholipids is the consequence of saturation directed to the acyl chains of the incorporated phospholipids.  相似文献   

6.
Fatty chain composition of phospholipids in sea urchin spermatozoa   总被引:1,自引:0,他引:1  
1. An analysis was made of lipids extracted from the spermatozoa of the sea urchins, Hemicentrotus pulcherrimus and Anthocidaris crassispina. 2. Nearly all the lipids from both species consisted of phospholipids (about 80%) and cholesterol (about 14%). Triglyceride and cholesterol ester were present in trace amounts. 3. The fatty acid composition of each phospholipid was determined by gas-liquid chromatography. In both species, the fatty acid consisting of phosphatidylethanolamine was of the unsaturated type for the most part, while cardiolipin was comprised to a considerable degree of saturated fatty acids. In phosphatidylcholine and phosphatidylserine from H. pulcherrimus sperm, unsaturated fatty acid content was somewhat higher than that in phospholipids from A. crassispina sperm.  相似文献   

7.
The fatty acid composition of human skin fibroblasts grown in 10% dialyzed fetal calf serum can be modified considerably by adding supplemental fatty acids to the culture medium. The degree of modification was dependent on the concentration of added fatty acid over the range tested, 2.5 X 10(-5) to 1 X 10(-4) M. At the higher concentration, the extent of the modifications was as those which can be produced in nonhuman or malignant cell lines. Although the greatest changes were produced in the neutral lipid fraction, the cellular phospholipids also exhibited appreciable modifications. The phospholipids isolated from a microsomal fraction prepared from the cell homogenate exhibited similar changes in fatty acyl composition. These findings indicate that the human fibroblast can tolerate considerable variability in fatty acid composition, even in membrane phospholipids. The triglyceride content of the cells increased when they were grown in the presence of added fatty acids, but the phospholipid and cholesterol content remained unchanged. Growth was not affected by either oleic or linoleic acids, but it was reduced up to 50% when palmitic linolenic, or arachidonic acid was added in concentrations of 5 X 10(-5) M or above. Extensive modifications in phospholipid fatty acid composition also were produced in confluent monolayers of these fibroblasts. This suggest that some membrane lipid turnover occurs even when the cultures are not rapidly growing. Fatty acid modifications also were produced in the commercially available IMR-90 strain of human lung fibroblasts, suggesting that the ability to tolerate considerable differences in fatty acid composition is not a special property of the skin fibroblast line that was isolated locally.  相似文献   

8.
Whole serum obtained from hypercholesterolemic rhesus monkeys was found to stimulate cholesterol esterification and cholesteryl ester accumulation in rhesus monkey arterial smooth muscle cells in culture to a significantly greater extent than normocholesterolemic serum. This was true even when the cholesterol concentration of the culture medium was equalized. Isolation and characterzation of the low density lipoproteins (LDL) from rhesus monkeys indicated that the LDL from hypercholesterolemic animals was 33% larger than LDL from normocholesterolemic animals due principally to an increase in the amount of cholesteryl ester per molecule. As a result, LDL from hypercholesterolemic animals transported over 50% more cholesterol per molecule than did normal LDL. The LDL of altered composition from hypercholesterolemic animals, when added to smooth muscle cells in culture, was nearly twice as effective in stimulating cholesterol esterification and cholesteryl ester accumulation than was LDL of normal composition. Results suggest that at least part of the exaggerated ability of whole hypercholesterolemic serum to stimulate the esterification and accumulation of cholesterol in cells in culture is due to the presence of LDL of altered composition.  相似文献   

9.
Physical and chemical criteria of lipoproteins containing apolipoprotein B, extracted from human aortic intima, were compared with those of plasma low density lipoproteins (LDL). Homogenates of grossly normal intima and advanced atherosclerotic lesions were subjected to differential ultracentrifugation to isolate a d = 1.006--1.063 g/ml density fraction which was extensively characterized. By electroimmunoassay, over 90% of the recovered apolipoprotein B immunological reactivity was found in isolates from both plaques and normal intima. In isolates of plaque and normal intima, particles of the same size as LDL were found, although a small population of very large structures was also present in plaque fractions. Apolipoprotein composition was similar to that of plasma LDL except for the presence of human serum albumin in aortic isolates. Fractions from aorta demonstrated greater electrophoretic mobilities than LDL. The lipid composition of isolates from normal intima was similar to that of LDL. The lipid composition of plaque fractions showed a significant decrease in the cholesteryl ester to free cholesterol ratio and in the triglyceride content in comparison to LDL and to fractions from normal intima. The fatty acid pattern of the cholesteryl ester fraction from isolates of both normal and plaque aortic homogenates demonstrated a significant decrease in the linoleate to oleate ratio as compared to LDL. Our initial studies suggest that althought aortic fractions are similar to LDL by certain criteria, some differences observed are more pronounced in fractions from lesions than from normal intima.  相似文献   

10.
1. Concentrations and compositions of liver, serum and milk lipids of cows were measured during 6 days' starvation and serum lipids during 60 days' re-feeding. 2. The concentration of free fatty acid in serum increased fivefold during starvation. 3. The content of total lipid in liver (g/100g of liver dry matter) doubled owing to a 20-fold increase in triglyceride, an eightfold increase in cholesterol ester, a three fold increase in free fatty acid and a 20% increase in cholesterol. There were no changes in the content or composition of liver phospholipids. 4. Starvation lowered the concentrations of total lipid, phospholipid and cholesterol ester of dextran sulphate-precipitable serum lipoproteins. Total lipid and cholesterol ester concentrations in lipoproteins of d greater than 1.055 and in lipoproteins not precipitable by dextran sulphate decreased from day 4 of the starvation period and during the first 20 days' re-feeding. 5. During starvation there were decreases in percentages of stearic acid and increases in oleic acid in serum free fatty acids and triglycerides and in liver neutral lipid. 6. Throughout starvation total milk lipid yield decreased, yields and percentages of C4-14 fatty acids decreased and percentages of C18 fatty acids increased. 7. It is suggested that accumulation of triglyceride in liver may be caused by increased uptake of plasma free fatty acids without corresponding increase in lipoprotein secretion.  相似文献   

11.
The structure of human serum low density lipoprotein (LDL) was investigated by perturbing the LDL structure with sodium dodecyl sulfate (SDS). The change in LDL structure induced by the addition of SDS was monitored by sedimentation velocity measurements, ultraviolet difference spectroscopy, fluorescence spectroscopy and proteolytic digestion of apo-LDL with subtilisin BPN' [EC 3.4.21.14]. As the concentration of SDS was increased from 0.1 mg/ml to 3 mg/ml with LDL concentrations between 2.0 mg/ml and 4.4 mg/ml, the sedimentation coefficient of LDL changed in three distinct steps. It was found by chemical analyses that not more than 30% of the total lipid was lost from LDL in the second step, whereas the final step in the change of sedimentation coefficient corresponded to the complete removal of apo-LDL from the constituent lipids of LDL. The ultraviolet difference spectrum between the native and SDS-treated LDL and the quenching of LDL fluorescence underwent about 80% of the total change while the SDS concentration was only sufficient to cause the second of the three step changes in sedimentation coefficient. SDS-polyacrylamide gel electrophoresis of apo-LDL treated with subtilisin BPN' also showed that more than 70% of apo-LDL became susceptible to proteolysis under the same conditions. These results were interpreted as indicating that the solubilization of 20 to 30% of the lipids on the surface of LDL exposed nearly 80% or more of apo-LDL to the solvent. A small portion of apo-LDL was, however, still firmly anchored to the remaining lipid micelle as long as the concentration of SDS was less than that required to cause the final step of the change in sedimentation coefficient.  相似文献   

12.
A 12-week dietary intervention was carried out among 40 families from North Karelia, a county in Finland with an exceptionally high rate of coronary heart disease and high serum cholesterol values. The proportion of dietary energy derived from fat was reduced during the 12-week intervention period from about 39% to 23% in all families. The families were randomly allocated into two groups. Twenty families consumed a diet with a polyunsaturated to saturated fat (P/S) ratio of 0.9 (group I), while the other 20 families had a diet with a P/S ratio of 0.4 (group II). Total serum cholesterol decreased by 16% and 9% in men of groups I and II, respectively, and by 16% in women of both groups. These changes were due to a decrease in both low density lipoprotein (LDL) and high density lipoprotein (HDL) cholesterol. LDL cholesterol and phospholipid reached minimum values after 6 weeks on both intervention diets, but LDL protein responded more slowly. Thus, after 6 weeks LDL had an altered composition containing less cholesterol and phospholipids and more protein and triglycerides than during the baseline diet. During the intervention, the linoleic acid content in the serum cholesteryl ester fraction increased, and the magnitude of this change correlated negatively with the changes in total and LDL cholesterol. The decrease in HDL cholesterol during the two intervention diets was due to a fall in the HDL2 cholesterol (29% and 24% in men, and 26% and 25% in women in groups I and II, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   

13.
Human endothelial cells (EA.hy 926 line) were loaded with cationized low density lipoprotein (LDL) and subsequently incubated with fatty acid/bovine serum albumin complexes. The fatty acids were palmitic, oleic, linoleic, arachidonic, and eicosapentaenoic acids. The preincubations resulted in extensively modified fatty acid profiles in cell membrane phospholipids and in cellular cholesteryl esters. The cholesterol efflux from these fatty acid-modified cells was measured using 0.2 mg high density lipoprotein3 (HDL3)/ml medium. The efflux was significantly higher for the palmitic acid-treated cells, compared to all other fatty acid treatments. These differences in efflux rates were not caused by changes in the binding of HDL3 to high affinity receptors on the EA.hy 926 cells. Efflux mediated by dimethyl suberimidate-treated HDL3, which does not interact with high affinity HDL receptors, was similar to efflux induced by native HDL3 after all fatty acid treatments. Our results indicate that high affinity HDL receptors are not important for HDL-mediated efflux of cell cholesterol. The fatty acid composition of the cell membrane phospholipids may be an important determinant.  相似文献   

14.
The effect of clofibrate and ethanol in the rat was studied on the following aspects of lipid composition and metabolism: liver delta 5, delta 6 and delta 9 fatty acid desaturases, fatty acid synthetase and fatty acid desaturase microsomal electron transport chain activity and serum cholesterol, triacylglycerols and high (HDL), low (LDL) and very low density lipoprotein (VLDL) levels. Clofibrate administered for 9 days (0.3% W/W) did not modify the relative composition of liver phospholipids and cholesterol, but did diminish triacylglycerol levels increased by ethanol. This effect could be explained by the possible beta-adrenergic blocking properties of clofibrate or by an increased activity of peroxisomal beta-oxidation. Clofibrate also promoted a decrease in serum cholesterol and triacylglycerol levels, delta 6 desaturase activity and a suppression of the electron transport chain as measured by NADH cytochrome b5 reductase and NADH cytochrome c reductase. The drug increased delta 9 desaturase activity and fatty acid synthetase, while no effect could be found in delta 5 desaturase activity. The hypocholesterolenic effect of clofibrate can not be explained through the delta 6 desaturase inhibition, or the fatty acid synthetase enhancement. Ethanol increased the HDL and VLDL and lowered LDL serum concentrations, while clofibrate reversed these results. Considering that clofibrate could have antiatherosclerotic effect in the rat, it is difficult to explain it through these changes in lipoprotein levels, since according to Miller and Miller low HDL levels are predictive of coronary heart disease.  相似文献   

15.
1. The lipids of rat heart, kidney, skeletal muscle and liver were separated by chromatography on silicic acid into cholesterol ester, triglyceride, free-fatty acid and phospholipid fractions. 2. The fatty acid compositions of these fractions were determined by gas–liquid chromatography. 3. Palmitic acid was always present in highest concentration in the cholesterol ester fraction; oleic acid was present in greatest percentage in the triglyceride fraction; arachidonic acid was in highest concentration in phospholipid, and in lowest concentration in triglyceride fractions. 4. The fatty acid compositions of the cholesterol ester fractions were broadly similar for all the extrahepatic tissues. 5. Some differences in fatty acid composition of the phospholipids were evident between the hepatic and extrahepatic fractions.  相似文献   

16.
《Experimental mycology》1983,7(3):216-226
Oospores and oospheres ofAchlya americana Humphrey were isolated by sonication and filtration through nylon-mesh cloth of progressively diminishing porosity, and their lipid composition was investigated. The average dry weight of an oospore was 3.2 ng. Approximately 37% of the dry weight was composed of lipid. Triacylglycerols represented 88.7% of the total lipid, unesterified fatty acids made up 9.7%, and sterols, sterol esters, phospholipids, and mono- and diacylglycerols each constituted less than 1% of the total. Palmitic, oleic, and linoleic acids were the predominant fatty acids, along with smaller amounts of myristic, palmitoleic, stearic, arachidonic, and eicosapentaenoic acids. The fatty acid composition of the triacylglycerol fraction was similar to that of the total lipid, while that of the phospholipid fraction was higher in oleic acid. The unesterified fatty acid fraction was higher in saturated components than the total lipid, while the sterol ester fraction was higher in unsaturated fatty acids. In both the total lipid and the various lipid classes, unsaturated fatty acids increased during spore development. The sterol fraction consisted of 72% fucosterol, 22% cholesterol, and 7% 24-methylenecholesterol. In both oospheres and oospores, 1-[14C] acetate was assimilated most readily into phospholipids, triacylglycerols, and unesterified fatty acids, and was incorporated preferentially into palmitic, palmitoleic, and oleic acids. 1-[14C]-Arachidonic acid was incorporated by isolated oospheres into eicosapentaenoic acid, indicating that arachidonic acid is the immediate precursor of eicosapentaenoic acid.  相似文献   

17.
The liver is a major source of the plasma lipoproteins; however, direct studies of the regulation of lipoprotein synthesis and secretion by human liver are lacking. Dense monolayers of Hep-G2 cells incorporated radiolabeled precursors into protein ([35S]methionine), cholesterol ([3H]mevalonate and [14C]acetate), triacylglycerol, and phospholipid ([3H]glycerol), and secreted them as lipoproteins. In the absence of free fatty acid in the media, the principal lipoprotein secretory product that accumulated had a density maximum of 1.039 g/ml, similar to serum low density lipoprotein (LDL). ApoB-100 represented greater than 95% of the radiolabeled apoprotein of these particles, with only traces of apoproteins A and E present. Inclusion of 0.8 mM oleic acid in the media resulted in a 54% reduction in radiolabeled triacylglycerol in the LDL fraction and a 324% increase in triacylglycerol in the very low density lipoprotein (VLDL) fraction. Similar changes occurred in the secretion of newly synthesized apoB-100. The VLDL contained apoB-100 as well as apoE. In the absence of exogenous free fatty acid, the radiolabeled cholesterol was recovered in both the LDL and the high density lipoprotein (HDL) regions. Oleic acid caused a 50% decrease in HDL radiolabeled cholesterol and increases of radiolabeled cholesterol in VLDL and LDL. In general, less than 15% of the radiolabeled cholesterol was esterified, despite the presence of cholesteryl ester in the cell. Incubation with oleic acid did not cause an increase in the total amount of radiolabeled lipid or protein secreted. We conclude that human liver-derived cells can secrete distinct VLDL and LDL-like particles, and the relative amounts of these lipoproteins are determined, at least in part, by the availability of free fatty acid.  相似文献   

18.
Abstract— Cholesterol esters were isolated from cerebral cortex and white matter of patients with Schilder's disease, GM1-gangliosidosis and Tay-Sachs disease, and the fatty acid composition was determined by gas-liquid chromatography. The fatty acid composition was similar among the three pathological conditions, but it was entirely different from that reported for cholesterol esters of normal brain. Lecithin and ethanolamine phospholipids were isolated from the same brain specimens, treated with snake venom phospholipase A, and the fatty acids at the a’and β-positions of the glycerol moiety were determined separately. The fatty acid composition of cholesterol esters was similar to that of the β-position fatty acids of lecithin of white matter in all samples, and was quite different from those of the a'-position of lecithin, or of the a’or β-position of ethanolamine phospholipids. The results indicate that the source of fatty acids for cholesterol esterification in nonspecific sudanophilic demyelination is different from that in normal brain, and that the most likely source is the β-linked fatty acids of lecithin. There are two possible enzymic mechanisms; activation of phospholipase A and subsequent esterification of the liberated β-position fatty acids to cholesterol, or direct transacylation by lecithin-cholesterol acyl transferase.  相似文献   

19.
Although liver fatty acid-binding protein (L-FABP) is an important binding site for various hydrophobic ligands in hepatocytes, its in vivo significance is not understood. We have therefore created L-FABP null mice and report here their initial analysis, focusing on the impact of this mutation on hepatic fatty acid binding capacity, lipid composition, and expression of other lipid-binding proteins. Gel-filtered cytosol from L-FABP null liver lacked the main fatty acid binding peak in the fraction that normally comprises both L-FABP and sterol carrier protein-2 (SCP-2). The binding capacity for cis-parinaric acid was decreased >80% in this region. Molar ratios of cholesterol/cholesterol ester, cholesteryl ester/triglyceride, and cholesterol/phospholipid were 2- to 3-fold greater, reflecting up to 3-fold absolute increases in specific lipid classes in the order cholesterol > cholesterol esters > phospholipids. In contrast, the liver pool sizes of nonesterified fatty acids and triglycerides were not altered. However, hepatic deposition of a bolus of intravenously injected [14C]oleate was markedly reduced, showing altered lipid pool turnover. An increase of approximately 75% of soluble SCP-2 but little or no change of other soluble (glutathione S-transferase, albumin) and membrane (fatty acid transport protein, CD36, aspartate aminotransferase, caveolin) fatty acid transporters was measured. These results (i) provide for the first time a quantitative assessment of the contribution of L-FABP to cytosolic fatty acid binding capacity, (ii) establish L-FABP as an important determinant of hepatic lipid composition and turnover, and (iii) suggest that SCP-2 contributes to the accumulation of cholesterol in L-FABP null liver.  相似文献   

20.
Lipid composition and lipid metabolism of Spiroplasma citri.   总被引:3,自引:10,他引:3       下载免费PDF全文
In a horse serum-based medium containing a full complement of fatty acids, cells of Spiroplasma citri were seen to preferentially incorporate palmitic acid. In the same medium, which had a steryl ester-to-sterol ratio of 3.64, a steryl ester-to-sterol ratio of 0.23 was seen in the cells, cholesterol being preferentially incorporated over cholesteryl ester. Like most other mycoplasmas, S. citri was shown to be unable to synthesize fatty acids or esterify cholesterol. The neutral lipids of S. citri grown in a medium containing horse serum consisted of free cholesterol, cholesteryl ester, free fatty acids, triglycerides and diglycerides. All polar lipids were phospholipids, with no glycolipids detected. These phospholipids, which are characteristic of many mycoplasmas, are phosphatidyl glycerol, diphosphatidyl glycerol, and their lyso derivatives. Sphingomyelin was also incorporated when cells were grown on horse serum. A sterol requirement for the growth of S. citri was confirmed using a serum-free medium supplemented with bovine serum albumin, palmitic acid, and various concentrations of sterols dissolved in Tween 80. The addition of palmitic acid stimulated growth but was not essential for growth. S citri was shown to grow best on cholesterol and beta-sitosterol and was able to grow on stigmasterol and ergosterol to a lesser degree. No growth was obtained using mevalonate, deoxycholate, or taurodeoxycholate as an alternative to sterol. S. citri was also able to grow when palmitic acid was replaced with oleic acid, linoleic acid, or linolenic acid. Alterations in the lipid composition of the growth medium and hence in the lipid composition of S. citri induced changes in the characteristic helical morphology of the cells, concurrent with loss of cell viability. Culture, age, and pH were also factors in determining cell morphology and viability.  相似文献   

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