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At least 883 records · Page 49Linked to original sources
PubMed1988

Hormone-sensitive lipase is involved in the hydrolysis of lipoidal derivatives of estrogens and other steroid hormones.

Long-chain fatty acid esters of 17 beta-estradiol and other steroid hormones, which are formed in hormone-sensitive tissues, can be regenerated to the free hormone by the action of an esterase present in the cytosol. This esterase has now been examined in bovine placenta cotyledons. Activity towards steroid fatty acid esters was accompanied by activity towards a diacylglycerol analogue and cholesteryl oleate. During purification procedures, the ratio of activities towards the diacylglycerol analogue and estradiol 17 beta-oleate remained approximately constant. Activity towards these two substrates was inhibited by increasing concentrations of HgCl2 and phenylmethanesulfonyl fluoride in a parallel manner. Upon treatment with [3H]diisopropyl fluorophosphate, a major labelled species of Mr approx. 84,000 was formed. Activation by ATP and the catalytic subunit of cAMP-dependent protein kinase occurred. These properties were very similar to those of the hormone-sensitive lipase of bovine adipose tissue previously reported and run in parallel in this study. A highly purified preparation of this latter enzyme was found to hydrolyse steroid fatty acid esters and relative activities towards such substrates, diacylglycerol analogue and cholesteryl oleate, were similar to the placenta esterase. When the two esterases were phosphorylated with [gamma-32P]ATP, a labelled species of Mr 84,000 was isolated in both cases by use of an antibody raised against purified hormone-sensitive lipase of bovine adipose tissue. It is concluded that hormone-sensitive lipase is very likely the enzyme responsible for hydrolysis of steroid fatty acid esters in bovine placenta and possibly steroid hormone target tissues in general.

Androgens↗
PubMed1987

Convertibility of a saponifiable lipoidal derivative of 18-hydroxycorticosterone.

Metabolic properties and subcellular localization of the biosynthesis of SM, a saponifiable 18-OH-B (18-Hydroxycorticosterone) derivative, were investigated. Homogenates biosynthesized SM at a nearly constant rate of 463 pmol/50 mg tissue during 30 min. This biosynthesis was more efficient at pH 7.4 than at pH 4.8. Not only 18-OH-B but also its less polar anhydride 18-DAL (18-Deoxyaldosterone) were good precursors. SM was reverted to these precursors both enzymatically and spontaneously, 4.8 being a more suitable pH for this reversion than 7.4. Trapping experiments demonstrated a sequence comprising, in this order, the following echelons: SM, 18-OH-B, 18-DAL, Aldosterone. The first two steps are reversible and the last two ones depend on proton concentrations. It is postulated that SM could be on a dead-end to which 18-OH-B could be deviated if Aldosterone biosynthesis became temporarily unnecessary. Also, that 18-OH-B may convert to either 18-DAL or SM for selective membrane transports, according to homeostatic requirements.

18-Hydroxycorticosterone↗
PubMed1987

Selective turnover of the essential fatty acid ester components of estradiol-17 beta lipoidal derivatives formed by human mammary cancer cells in culture.

The properties of fatty acyl coenzyme A: estradiol-17 beta acyl transferase in microsomes derived from pooled human mammary cancer tissue have been examined. A pH optimum of 5.5 was found and addition of long-chained fatty acyl CoAs increased estradiol-17 beta (E2) 17-monoacyl ester synthesis; the apparent Km for E2 being 8 microM when oleoyl CoA, linolenoyl CoA or palmitoyl CoA were employed. Testosterone, dehydroepiandrosterone, and 5-androsterone-3 beta, 17 beta-diol acted as competitive inhibitors with Ki values of 36, 36 and 46 microM, respectively. The composition of E2 fatty acyl esters (E2-L) formed by incubation of [3H]E2 with human mammary cancer tissue and human mammary cancer cell lines has been determined by HPLC. Although the composition of E2-L in estrogen receptor negative cell lines (MDA-MB-231 and MDA-MB-330) was generally similar to that found for MCF-7 cells (estrogen receptor positive) and pooled human mammary cancer tissue, the former cell lines contained a 3-fold higher relative concentration of E2-17 beta stearate. MCF-7 cells were exposed to 30 nM [3H]E2 and the composition of the isolated [3H]E2-L fraction studied at various time intervals. At 0.5 h, the intracellular concentration of E2-L was 1.8 +/- 0.4 (SEM) pmol/mg DNA which increased to values of 3.6 +/- 0.6 and 4.3 +/- 0.5 at 4 h and 16 h, respectively. In the subsequent 3 h following transfer to medium lacking [3H]E2, the concentration of E2-L declined to 3.7 +/- 0.3 pmol/mg DNA. The subfraction of E2-L composed of E2-17 beta arachidonate, linolenate and docosahexaenoate, was seen to decline in relative abundance after 0.5 h and to reach significantly lower relative levels at 16 h, and again in the 3 h period following estrogen withdrawal. The data suggests that these components, derived from essential fatty acids, are more metabolically active. This may then provide a new lead to link these novel estrogen derivatives with the established relationship between unsaturated fatty acids and an increased mammary cancer incidence.

Acyl Coenzyme A↗
PubMed1983

Significance of lipoidal estradiol in human mammary tumors.

Incubations of p-nitrophenyl fatty acyl esters and estradiol-17 beta fatty acyl 17-esters with porcine esterase, human mammary tumor cytosol and rat uterine cytosol leads to ester hydrolysis of compounds with short chain fatty acids. Esters with long chain fatty acids show no hydrolysis except in the presence of Tween 80. Short chain fatty acid esters have a higher binding potency to the estrogen receptor than long chain fatty acid esters. Extraction of the nuclear receptor peak sedimenting at 4.6S and identification of the steroid showed that about 90% of the radioactivity was associated with estradiol and only 10% with estradiol esters. These studies show that estradiol fatty acyl esters act as a storage form from which estradiol is released by enzymatic hydrolysis.

Animals↗