Nonsaponifiable Lipid Synthesis Research Articles

Cholesterogenesis and cell division in phytohemagglutinin-stimulated human lymphocytes: a comparative study with several inhibitors

It has been shown that when lymphocytes are stimulated by phytohemagglutinin the expected stimulation of DNA synthesis is preceded by stimulation of cholesterol synthesis. This confirms the existence of a relation between cell division and cholesterol synthesis. We studied the effect on cell division of six inhibitors of cholesterol biosynthesis, previously shown to interfere with different steps of the process: 7β-hydroxycholesterol, 25-hydroxycholesterol, lanost-7-en-3β,32-diol, mevinolin, propiconazole, dodecylimidazole. Since experiments were performed in the presence of a high percentage of human serum, which provided cells with exogenous cholesterol via the LDL-receptor pathway, our investigation was focused on the role of newly synthesized cholesterol. The biosynthesis was evaluated by labeling cells with [ 14C]sodium acetate; to take into account variations of cell permeability to sodium acetate, the results were expressed as the percentage of total cellularly incorporated radioactivity transformed into cholesterol, after separation from all other labeled metabolites. These data were compared with the percentage of transformation into nonsaponifiable lipids, which varied in parallel with HMG-CoA reductase activity, as confirmed by direct enzymatic measurement. Cell division was assessed by simultaneous measurements of three parameters: thymidine incorporation into DNA, cell proliferation and cellular protein content. All the effectors strongly inhibited the conversion of labeled acetate into cholesterol, but cell division was not inhibited by two of them: propiconazole and 7β-hydroxycholesterol. These compounds only slightly inhibited the synthesis of nonsaponifiable lipids, which mainly consisted of methylsterols resulting from a blockage of lanosterol demethylation. Thus, it can be concluded that the nonsaponifiable metabolite essential for cell growth is not newly synthesized cholesterol. It was also found that inhibitors affected cell division only when they were added to the culture medium before the decline of cholesterol synthesis stimulation.

Hepatic and intestinal formation of polar sterols in vivo in animals fed on a cholesterol-supplemented diet.

In rats fed on a diet containing 1% cholesterol for 24 h, the decrease in hepatic non-saponifiable lipid synthesis, cholesterogenesis and 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was accompanied by an increase in the proportion of newly synthesized polar sterols in vivo. In these animals there was also a strong inverse correlation between the proportion of polar sterols in the non-saponifiable lipid and hepatic HMG-CoA reductase activity. A similar correlation was not observed in animals fed on a normal diet. Cholesterogenesis in the intestine was not as sensitive to inhibition by dietary cholesterol as was that in the liver, and there was no increase in the polar-sterol content of the newly synthesized non-saponifiable-lipid fraction.

Contribution of the shunt pathway of mevalonate metabolism to the regulation of cholesterol synthesis in rat liver.

The modulation of the shunt pathway of mevalonate metabolism (Edmond, J., and Popják, G. (1974) J. Biol. Chem. 249, 66-71) has been studied in livers from fed, starved, and diabetic rats perfused with a physiological concentration (300 nM) of [5-14C] + [5-3H]mevalonate. Shunt activity was measured by (i) production of 14CO2 (corrected for loss of label by exchange reactions) and (ii) production of 3H2O. Contribution of exogenous mevalonate to total mevalonate production (0.06-0.11%) was assessed in parallel experiments by the incorporation of 3H2O into sterols. Inhibition of non-saponifiable lipid synthesis by starvation and diabetes is not associated with an inhibition of mevalonate production but with a major increase in shunting (7-34%) of sterol-bound mevalonate. The shunt pathway of mevalonate metabolism appears to participate in the regulation of cholesterol synthesis.

The effect of vitamin D status on cutaneous sterologenesis in vivo and in vitro

Recent studies have shown that cutaneous sterologenesis is autonomous from the influence of circulating sterols, and that the epidermis is an important site of sterologenesis which is regulated by permeability barrier requirements. In addition to barrier function, an additional, important function of the epidermis is to synthesize sterol precursors of vitamin D 3. The present study was designed, first, to determine whether vitamin D status and/or circulating levels of 1,25-dihydroxyvitamin D 3 might play a role in regulating cutaneous sterol synthesis in vivo and, second, whether 1,25-dihydroxyvitamin D 3 modulates sterologenesis in cultured human keratinocytes. Hairless mice were maintained on a vitamin D-deficient diet in the dark and supplemented with various doses of vitamin D 3/day. Despite demonstrating serum 25-hydroxyvitamin D 3 levels ranging from < 10 to 343 ng/ml, the incorporation of tritiated water into cholesterol and total nonsaponifiable lipids in both the epidermis and dermis was similar in the four groups of animals. Likewise, administration of various doses of 1,25-dihydroxyvitamin D 3 to vitamin D-deficient mice resulted in serum levels of 1,25-dihydroxyvitamin D 3 ranging from < 10 to 85 pg/ml; yet, cholesterol and total nonsaponifiable lipid synthesis was similar in both the dermis and epidermis in all groups of animals. Moreover, administration of 0.6 μg/kg per day of 1,25-dihydroxyvitamin D 3 to ‘normal’ vitamin D-replete mice also had no effect on cutaneous sterol synthesis. Furthermore, conversion of 7-dehydrocholesterol to cholesterol in vitamin D-deficient vs. supplemented animals did not differ. Finally, addition of 1,25-dihydroxyvitamin D 3 to cultured keratinocytes over a concentration range of 10 −12–10 −7 M did not affect sterologenesis, except at supraphysiologic doses (10 −7 M). Together, these results suggest that vitamin D status does not influence sterol synthesis in the skin.

Effect of Essential Fatty Acid Deficiency on Cutaneous Sterol Synthesis

The fact that the skin is a major site of total body sterologenesis, coupled both with the apparent absence of low density lipoprotein receptors on keratinocytes and with the lack of influence of serum cholesterol on epidermal sterologenesis, has created the impression that epidermal lipid synthesis might be autonomous, i.e., nonregulatable. Recent studies have shown, however, that disruption of cutaneous barrier function with acetone or detergents stimulates epidermal sterologenesis (J Lipid Res 26:418-427, 1985). To correlate further sterologenesis with barrier function, we measured de novo synthesis of cholesterol and total nonsaponifiable lipids in essential fatty acid-deficient (EFAD) hairless mice. Animals with defective barrier function, manifested by abnormal transepidermal water loss, demonstrated a 2-fold increase in epidermal cholesterol and total nonsaponifiable lipid synthesis over controls while synthesis in the dermis was unchanged. Epidermal sterologenesis in EFAD animals, repleted with linoleic acid either systematically or topically, returned toward normal as barrier function improved. Moreover, plastic occlusion of EFAD mouse skin normalized epidermal sterologenesis at 1 and 3 days. These results provide further evidence that epidermal sterologenesis is not entirely autonomous, and can be regulated by water barrier requirements.

De novo sterologenesis in the skin. II. Regulation by cutaneous barrier requirements.

Recent studies suggest: that the epidermis and pilosebaceous epithelium are important sites of de novo sterol synthesis, and that the rate of cutaneous cholesterol synthesis does not change with alterations in circulating sterol levels. Since cutaneous sterols may be important for permeability barrier function, we studied the effect of experimentally altered barrier function on de novo sterologenesis in the epidermal and dermal layers of the skin. Epidermal sterologenesis appeared to be modulated by the skin's barrier requirements because topical detergent and acetone treatment stimulated de novo synthesis of nonsaponifiable lipids in the epidermis, but not in the dermis. Synthetic activity paralleled both the return of barrier function toward normal and the extent of prior damage to the barrier. Moreover, plastic-wrap occlusion of solvent-treated sites simultaneously corrected both the barrier abnormality and normalized sterol synthesis, further linking increased epidermal sterologenesis to barrier requirements. Whereas topical applications of a variety of other topical lipids did not down-regulate synthesis, epicutaneously applied 25-hydroxycholesterol appeared to diminish synthesis. These results suggest that maintenance of barrier function is one purpose of epidermal de novo nonsaponifiable lipid synthesis, and demonstrate further that, despite a lack of low density lipoprotein receptors, epidermis can regulate its lipid-synthetic apparatus in response to certain specific requirements.

Localization of De Novo Sterologenesis in Mammalian Skin

Previous studies have demonstrated that the skin is an important site of de novo sterol synthesis and that there is a sex difference in cutaneous sterologenesis with male animals synthesizing more sterols than females. The aim of the present study was to localize the major sites of sterol synthesis within the skin and to determine which of these sites accounted for the sex differences in sterologenesis. In male and female rats whose dermal and epidermal layers are separated by dithiothreitol treatment, the dermis is the major site of skin sterologenesis (males 86% of total, females 82% of total). Moreover, the sex difference in skin sterol synthesis is quantitatively localized primarily within the dermal layer (approximately 2.5-fold greater in the dermis of males). Sterol synthesis is also increased in the epidermis of males. To rule out the possibility that sebaceous gland production accounted for our observations, we treated animals with isotretinoin (13-cis-retinoic acid), a drug that suppresses sebaceous gland sebum production. Sterol synthesis in the skin of both male and female rats is not significantly altered by isotretinoin administration and the sex difference in skin sterologenesis is unaffected. To further localize the sites of sterol synthesis within the skin, studies of hairless mice whose skin was split by DTT were initiated. In hairless mice, DTT separates the epidermis into upper (stratum corneum and granulosum) and lower (basal and spinous cells) strata. The basal layer was separated from the dermis by gentle scraping. As in rats, the dermis is the chief site of sterol synthesis in the skin. In addition, the lower layer of the epidermis (basal and spinous cells) is also a very active site of sterologenesis, accounting for 20% of total skin nonsaponifiable lipid synthesis. The upper epidermis accounted for only a small portion of total skin synthesis. It is highly likely that the bulk of cutaneous sterol synthesis occurs in the pilosebaceous epithelium.

The effect of uremia on circulating mevalonate metabolism in rats

Mevalonate, an essential intermediate in cholesterol synthesis, is metabolized either to sterols or by the shunt pathway to CO 2. Previous studies have demonstrated that the kidneys are the chief site of circulating mevalonate metabolism by both pathways. Following nephrectomy, as expected, the shunt pathway was reduced by greater than 50%. However, nephrectomy resulted in an enhancement of total body sterologenesis which was due to a marked stimulation of both liver and carcass sterol synthesis. The present study unexpectedly demonstrates that, even in the presence of intact kidneys, uremia induces marked alterations in the metabolism of circulating mevalonate that are similar to those observed following nephrectomy. In rats with normal renal mass the oxidation of mevalonate to CO 2 is reduced by 57% in acutely uremic and by 34% in chronically uremic animals. This reduction in shunt pathway activity directly correlates with the degree of impairment of renal function as measured by plasma BUN and creatinine levels. In contrast to the inhibition of the shunt pathway, acute and chronic uremia is associated with a two- to threefold increase in both hepatic and carcass cholesterol and nonsaponifiable lipid synthesis from circulating mevalonate. In the liver this enhancement of sterologenesis directly correlates with plasma BUN and creatinine concentrations. Renal sterologenesis from circulating mevalonate is not significantly altered by either acute or chronic uremia. This study demonstrates that uremia per se greatly alters circulating mevalonate metabolism resulting in a marked reduction in the shunt pathway and a large stimulation of sterol synthesis in both the liver and carcass.

Differences in de novo cholesterol synthesis between the intact male and female rat.

Three different isotopes were used to quantify de novo sterologenesis in intact male and female rats. All three substrates (i.e. [14C]acetate, [14C]octanoate, and [3H]water) were incorporated into nonsaponifiable lipids and cholesterol at significantly greater rates in males than in females. Even with cholesterol feeding, male animals synthesized significantly more cholesterol and nonsaponifiable lipids than females. The primary site of this sex difference in sterologenesis is extrahepatic, extraintestinal tissues (e.g. carcass). In the carcass this sex difference is chiefly due to an enhancement of sterol synthesis in the skin of male rats. Cholesterol synthesis is 73% greater and nonsaponifiable lipid synthesis is 85% greater in the skin of males than in females. Moreover, de novo sterologenesis in skin is hormonally dependent. In castrated females, testosterone treatment results in a 2-fold stimulation of skin sterol synthesis compared to that in animals administered estradiol or oil vehicle alone. In castrated males, estradiol treatment caused a 30% reduction in skin cholesterol and nonsaponifiable lipid synthesis compared to that in animals administered testosterone. The effects of sex steroid hormones on skin are, therefore, probably responsible for mediating the observed sex difference in de novo sterol synthesis. Additionally, this study demonstrates that the administration of estradiol and testosterone in physiological doses to castrated animals has no effect on cholesterol or nonsaponifiable lipid synthesis in liver, intestine, or other nondermal tissues.

Ketone bodies, glucose and glutamine as lipogenic precursors in human diploid fibroblasts.

Incorporation of [14C] from acetoacetate, D(-)- and L(+)-3-hydroxybutyrate, glucose, glutamine, acetate and palmitate in cellular lipids were studied in cultures in human diploid fibroblasts (HDF). The results showed that acetoacetate was 2-10 times more effective as a lipogenic precursor than was either D- or L-3-hydroxybutyrate. Its extent of incorporation into lipids was 2- to 8-fold more than the other precursors examined under conditions when the overall rates of nonsaponifiable and saponifiable lipogenesis as measured by 3H2O incorporation were essentially unchanged. Acetoacetate supported both saponifiable and nonsaponifiable lipid synthesis with half-saturation values (Km app.) of 185 microM and 30 microM, respectively. Glucose stimulated acetoacetate incorporation into lipids whereas, conversely, acetoacetate inhibited [14C]glucose incorporation into lipids. The presence of low density lipoproteins (LDL) cholesterol (40 microgram cholesterol/mL) inhibited the incorporation of [14C] from acetoacetate 56% into nonsaponifiable lipids; the inhibition was consistently higher (75%) when [14C]glucose or glutamine were the precursors. The loss of 3-hydroxy-3-methyl-glutaryl CoA (HMG CoA) reductase activity upon addition of LDL-cholesterol was greater than the suppression of [14C] incorporation from acetoacetate or glucose into nonsaponifiable lipids. In the presence of glucose, [14C]acetoacetate was incorporated into 3-beta OH sterols (digitonin precipitable) 7.7 +/- 1.1 times more effectively than was [14C]glucose. The results suggest that HDF would be a suitable model to investigate the effects of various precursors of HMG CoA on the rate of cholesterol biosynthesis.

The effect of decreased plasma cholesterol concentration on circulatinga mevalonate metabolism in rats.

Circulating mevalonate is metabolized by two mechanisms: the sterol pathways leading to cholesterol and the shunt pathway resulting in CO2 production. The kidney is the chief site of circulating mevalonate metabolism by both pathways. The present study investigated the effect of plasma cholesterol concentration on circulating mevalonate metabolism. 3-Aminopyrazolo(3,4-d)pyrimidine and Triton WR 1339 were utilized to induce "functional hypocholesterolemia". An enhancement of both renal total nonsaponifiable lipid synthesis (36-43%) and cholesterol synthesis (42%) from circulatinga mevalonate was observed when "functional hypocholesterolemia" was induced by either compound. Hepatic total nonsaponifiable lipid synthesis from circulating mevalonate was not enhanced in the Triton-treated animals, but 4-aminopyrazolo(3,4-d)pyrimidine treatment increased accumulation of total labeled nonsaponifiable lipids and cholesterol. No increase in labeled total nonsaponifiable lipids or cholesterol in the carcass was observed after treatment with wither compound. "Functional hypocholesterolemia" reduced the shunt pathway of circulating mevalonate metabolism by approximately 30%. This reduction occurred in both the renal and extrarenal shunt pathways. These data indicate that plasma cholesterol concentration regulates the in vivo metabolism of circulating mevalonate in that hypocholesterolemia reduces the shunt pathway and stimulates sterologenesis, and effect chiefly localized to athe kidneys.

Mevalonate metabolism in pregnant rats

Mevalonate is converted to cholesterol by the sterol pathway or can be oxidized to CO 2 by the shunt pathway; the kidneys are the chief site of mevalonate metabolism in both pathways. Recently, a major sex difference in circulating mevalonate metabolism has been observed in rats and in humans; in rats, females oxidized mevalonate to CO 2 at twice the rate of the males, but males converted mevalonate to cholesterol to a greater extent than did females. Sex hormones are believed to mediate these sex differences in mevalonate metabolism. In rats and humans, the hypercholesterolemia associated with pregnancy begins in the second trimester and reaches a maximum at term. The present study was undertaken to determine if alterations in the metabolism of circulating mevalonate occur during pregnancy. In 12-day pregnant animals, the metabolism of circulating mevalonate by the shunt pathway was increased (116 nmole mevalonate converted to CO 2 versus 94.6 nmole in control animals), whereas in the 18-day pregnant animals the shunt pathway was decreased below control values (72.9 nmole). Associated with this decrease in circulating mevalonate metabolism by the shunt pathway in the 18-day pregnant animals was an increase in the synthesis of nonsaponifiable lipids in the liver (26.8 versus 21.5 nmole of mevalonate incorporated). These changes correlated with the period of maximal hypercholesterolemia in pregnant rats. The increase in circulating mevalonate metabolism by the shunt pathway in 12-day pregnant animals was accompanied by a decrease in total body nonsaponifiable lipid synthesis (259.3 nmole of mevalonate converted by controls versus 235.1 nmole by 12-day pregnant rats). Renal sterol synthesis from circulating mevalonate was unaffected by pregnancy. The fetuses and placentas of the 12-day and 18-day pregnant animals converted circulating mevalonate to nonsaponifiable lipids, primarily cholesterol, indicating that maternal circulating mevalonate serves as a source of cholesterol for the fetus and the placenta. This study demonstrates that the metabolism of circulating mevalonate is influenced by pregnancy and that circulating maternal mevalonate is a precursor of fetal and placental cholesterol.

Synthesis of fatty acids and cholesterol by liver, adipose tissue and intestinal mucosa from obese and control patients.

Biopsies of adipose tissue, liver and small bowel mucosa obtained from grossly obese and control subjects were used to study absolute rates of fatty acid, cholesterol, and other nonsaponifiable lipid synthesis using glucose as substrate and 3H2O as the isotopic marker. Fatty acid synthesis in subcutaneous adipose tissue expressed on a cell basis was greater in obese than control subjects and was stimulated by a high concentration of insulin (1000 micro U/ml), but not by a lower amount (100 micro U/ml). Fatty acid synthesis in omental adipose tissue exceeded by 3-fold that of subcutaneous fat. Fatty acid synthesis in obese liver was twice that of control liver and 20 times greater than obese adipose tissue. In terms of total organ activity fatty acid synthesis in fat tissue equalled or exceeded that of liver in both obese and control subjects. The cholesterol content of obese adipose tissue 1.86 +/- 0.11 mg/g exceeded that of controls 1.47 +/- 0.07 mg/g. All tissues examined synthesized cholesterol and nonsaponifiable lipids, liver greater than adipose tissue greater than small bowel mucosa. Nonsaponifiable lipid synthesis per gram of adipose tissue or liver was similar in obese and control tissue. The synthesis of total nonsaponifiable lipids including sterols, hydrocarbons and squalene was appreciable in adipose tissue and was approximately 15% of that of liver. However, cholesterol synthesis in the liver exporessed in terms of total organ activity was 50 times that in adipose tissue. The study demonstrates by direct comparison that liver is the dominant cholesterogenic organ in man and also shows that adipose tissue is a significant site of formation of fatty acids and nonsaponifiable lipids.

Investigation of the fatty acid composition of the snail Succinea putris L.

1. 1. The incorporation of 1- 14C-acetate into some classes of lipids by Succinea putris L. is investigated. 2. 2. This snail is able to synthesize fatty acids from injected acetate. 3. 3. The acetate is also used for the synthesis of non-saponifiable lipids. 4. 4. The fatty acid composition of these animals is discussed.

Significance of Adipose Tissue and Liver as Sites of Fatty Acid Synthesis in the Pig and the Efficiency of Utilization of Various Substrates for Lipogenesis

A combination of in vivo and in vitro techniques as well as the assay of the activity of several enzymes presumably involved in lipogenesis have been employed to study the relative importance of liver and adipose tissue in overall fatty acid synthesis in the pig. Both the in vivo and in vitro results indicate that when glucose-U-14C is used as substrate, virtually all the newly synthesized fatty acids are formed in the adipose tissue. The incorporation of acetate-1-14C into liver fatty acids was, however, much greater than that of glucose-U-14C, suggesting that, if acetate was freely available in vivo, the contribution of liver to overall lipogenesis may be appreciable. Data on the activity of citrate cleavage enzyme and of three NADPH-generating dehydrogenase enzymes in liver and adipose tissue complement the results obtained in the lipogenic studies. The hepatic capacity for the production of cytoplasmic acetyl CoA from mitochondrially derived citrate is insignificant, as is its ability to generate NADPH required in the reductive synthesis of fatty acids. Collectively the results indicate that the adipose tissue plays a major, if not a nearly exclusive role in fatty acid synthesis in the pig. Nonsaponifiable lipid synthesis in the liver requires acetate rather than glucose as a starting substrate.

Effect of insulin of the in vitro synthesis of sterol and fatty acid by aorta and liver from diabetic rats

In the in vitro aorta intima-media preparation, glucose stimulates the synthesis of non-saponifiable lipids and fatty acids (FA), while addition of insulin has no effect. The synthesis of these lipids is depressed in aorta and liver from diabetic rats. Insulin treatment increases FA synthesis by aorta of diabetic rats only, but in liver of diabetic and normal animals insulin enhances the synthesis of FA and non-saponifiable lipids.

Factors affecting the metabolism of mevalonate by adipose tissue

1. 1. A 70-hr starvation reduced the incorporation of mevalonate into non-saponifiable lipids of epididymal fat pads, the small intestine and the liver of the rat. The rates in these tissues were 30, 40 and 24 per cent of those in the tissues of the fed rats. After 96 hr of refeeding the rates were restored to normal. Glucose and citrate failed to remove the starvation block in vitro. 2. 2. Human adipose tissue, the rat epididymal pads and the fat tail of the Syrian sheep utilized the potassium salt of mevalonic acid three to four times as efficiently as the lactone for the synthesis of non-saponifiable lipids. The optimal pH for the former two tissues is 6·6, and 7·7 for the fat tail. 3. 3. One mmolar concentration of 2:4-dinitrophenol and p-hydroxy-mercuribenzoate and 160 mmolar sodium fluoride and sodium malonate caused 94, 48, 97 and 100 per cent inhibition of mevalonate metabolism respectively. Taurocholate and glycocholate in a final concentration of 4 mmolar also inhibited the metabolism of mevalonate by 50 per cent. 4. 4. The saturation of an alkaline aqueous solution with sodium chloride and subsequent extraction with acetone, or acetone : petroleum ether (7:3) provided a rapid and quantitative procedure to extract all the metabolites of mevalonate.

Changes in lipid synthesis in rat liver during development

1. Lipogenesis, as measured by the incorporation of (14)C-labelled glucose or acetate into fatty acids in liver slices, is high in foetal and adult rat liver but is low in the liver of the suckling rat, especially with glucose as substrate. 2. The rate of synthesis of non-saponifiable lipids from glucose is about 15 times as great in the liver of the 18-day foetus as in adult liver. Activity in the newborn is negligible. 3. Glucose incorporation into fat is strongly concentration-dependent in liver slices from the adult and 2-week-old rat, but less markedly so in liver slices from the foetus. 4. Changes in the activity of hepatic citrate-cleavage enzyme (ATP-citrate lyase) occur in parallel with the changes in the extent of fatty acid formation, supporting the participation of this enzyme in lipogenesis. However, NADP-malate dehydrogenase, a potential source of reduced nucleotide coenzyme for lipogenesis in the adult, could not be detected in foetal rat liver.

The biosynthesis of squalene and sterols by the adipose tissue of rat, sheep and man

1. The subcutaneous and omental adipose tissue of man, the epididymal fat pads of the rat and the fat tail of the Syrian sheep incorporate mevalonic acid into non-saponifiable lipids. 2. Time studies showed that the rates of decarboxylation of mevalonic acid and synthesis of non-saponifiable lipids slightly decline after 20min. but subsequently remain linear for 6hr. 3. About one-half of the incorporated radioactivity in the non-saponifiable lipids was in squalene, 20% in lanosterol and cholesterol, and the remainder in unidentified substances.

METABOLISM OF MEVALONIC ACID BY LACTOBACILLUS PLANTARUM.

Durr, I. F. (American University of Beirut, Beirut, Lebanon), and A. N. Shwayri. Metabolism of mevalonic acid by Lactobacillus plantarum. J. Bacteriol. 88:361-366. 1964.-Lactobacillus plantarum strain 8014-H(2), unlike other lactobacilli studied, does not require mevalonic acid for growth, but growing and resting cells utilize it only for the synthesis of nonsaponifiable lipids. Upon the incubation of washed cells with mevalolactone-2-C(14), the label appeared in the lipids but not in CO(2). On the other hand, when mevalolactone-1-C(14) was used, the label appeared in CO(2) but not in lipids. For every mole of CO(2) liberated, 1 mole of radioactive carbon was introduced in the lipids, suggesting that terpenic polymers were synthesized. Amino acids did not stimulate the utilization of mevalonic acid. Starved cells could not synthesize nonsaponifiable lipids from mevalonic acid unless glucose was supplied. Sodium fluoride (0.14 m), 2,4-dinitrophenol (0.003 m), p-hydroxymercuribenzoate (0.0013 m), potassium phosphate (0.1 m), and ammonium formate (0.04 m) were potent inhibitors. Cells metabolized only one isomer of dl-mevalonic, and utilized the salt form at least twice as efficiently as the lactone. Optimal synthesis of lipids from mevalonic acid occurred aerobically, at pH 5 and 30 C.