Research paper
Properties of fatty acyl-coenzyme A: estradiol-17β acyltransferase in bovine placenta microsomes

https://doi.org/10.1016/0303-7207(88)90114-1Get rights and content

Abstract

The properties of the enzyme catalyzing the formation of non-polar derivatives of estradiol-17β (E2) esterified to long-chain fatty acids have been investigated in microsomal preparations from bovine placenta cotyledons. A rapid enzyme assay has been developed which involves simple solvent partitioning. The membrane-bound enzyme showed a pH optimum of 5.0 and addition of fatty acyl-coenzymes A (CoAs), such as oleoyl-CoA, palmitoyl-CoA and palmitoleoyl-CoA, increased [3H]E2-fatty acyl ester formation from [3H]E2 by some 7-fold. Linoleoyl-CoA, linolenoyl-CoA and arachidonoyl-CoA were much less effective as acyl donors. Only 17β-fatty acyl monoesters were synthesized in each instance. Similar results were obtained with microsomes or mitochondria from bovine endometrium. The apparent Km for E2 employing placenta microsomes was 8.0 ± 2.2 (SD) μM. Steroids such as testosterone, dehydroepiandrosterone and 5-androstene-3β,17β-diol acted as competitive inhibitors (Ki values 79, 46 and 39 μM, respectively). These, and other data to be reported separately, which showed that these steroids were substrates for the enzyme, demonstrate that the latter is not specific for E2. The [3H]E2-fatty acyl ester fractions biosynthesized from [3H]E2 and bovine placental or endometrial tissue were analyzed by high pressure liquid chromatography (HPLC) and were found to have similar compositions characterized by a high percentage of unsaturated fatty acids.

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    Citation Excerpt :

    More recently, Xu et al. studied the esterification of estradiol and other steroids in female rats [18]. In the rat liver, the highest specific estradiol acyltransferase activity was detected in the microsomal fraction, in accordance with previous studies [1], and Km was 4–6 μmol/l for estradiol at the optimal pH of 5, similarly to a previous study in bovine placental microsomes [19]. The lysosomal, nuclear and mitochondrial fractions contained about one third of the acyltransferase activity detected in the microsomal fraction, while no activity was detected in the cytosolic fraction [18].

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