THE BINDING OF HIGH AND LOW-DENSITY LIPOPROTEINS TO HUMAN PLACENTAL MEMBRANE-FRACTIONS
THE BINDING OF HIGH AND LOW-DENSITY LIPOPROTEINS TO HUMAN PLACENTAL MEMBRANE-FRACTIONS
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DOI：
10.1210/jcem-54-5-903
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发表时间：
1982-01-01
影响因子：
5.8
通讯作者：
OHASHI, M
中科院分区：
文献类型：
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作者：
CUMMINGS, SW;HATLEY, W;OHASHI, M
人胎盘滋养层细胞主要利用脂蛋白胆固醇进行孕酮的生物合成，并且胆固醇的从头合成速率很低。来自母体血浆低密度脂蛋白（LDL）而不是高密度脂蛋白（HDL）的胆固醇是胎盘胆固醇的主要来源。来自人胎盘的膜组分用于鉴定和表征HDL和LDL的特异性结合位点。用肝素预处理的膜组分导致[125 I]碘-LDL的特异性结合能力增加，是未用肝素预处理的膜组分的1.5倍。肝素预处理对胎盘膜[125 I]iodo-HDL的特异性结合能力无显著影响。[125 I]碘-LDL的特异性结合容量为107 ng LDL蛋白mg-1膜蛋白，在用肝素预处理的膜中Kd约为77 μ g LDL蛋白ml-1。对[125 I]碘-HDL的特异性结合能力大得多，等于323 ng HDL蛋白mg-1膜蛋白，Kd约为152 μ g HDL蛋白ml-1。每种[125 I]碘脂蛋白被相应的非放射性标记脂蛋白特异性置换。膜与胰蛋白酶和链霉蛋白酶的预孵育引起的[125 I]碘-LDL的特异性结合能力的88%和100%，分别减少。用肝素孵育膜会导致[125 I]碘-LDL的置换。然而，这些处理均不影响[125 I]碘-HDL结合能力。用胰蛋白酶消化人胎盘制备细胞并保持在单层培养中，证明[125 I]iodo-LDL和[125 I]iodo-HDL具有相似的结合位点。
Human placental trophoblastic cells use principally lipoprotein cholesterol for progesterone biosynthesis and the rate of de novo synthesis of cholesterol is low. Cholesterol derived from maternal plasma low density lipoprotein (LDL) rather than high density lipoprotein (HDL), is the principal source of placental cholesterol. Membrane fractions derived from human placenta were used to identify and characterize specific binding sites for both HDL and LDL. Pretreatment of membrane fractions with heparin resulted in an increase in the specific binding capacity for [125I]iodo-LDL 1.5 times that in membrane fractions not pretreated with heparin. Heparin pretreatment did not affect significantly the specific binding capacity of placental membranes for [125I]iodo-HDL. The specific binding capacity for [125I]iodo-LDL was 107 ng LDL protein mg-1 membrane protein, with an approximate Kd of 77 .mu.g LDL protein ml-1 in membranes pretreated with hepatin. The specific binding capacity for [125I]iodo-HDL was much greater, equal to 323 ng HDL protein mg-1 membrane protein, with an approximate Kd of 152 .mu.g HDL protein ml-1. Each [125I]iodolipoprotein was specifically displaced by the corresponding respective nonradiolabeled lipoprotein. Preincubation of membranes with trypsin and pronase caused reductions in the specific binding capacity for [125I]iodo-LDL of 88% and 100%, respectively. Incubation of membranes with heparin caused displacement of [125I]iodo-LDL. However none of these treatments affected [125I]iodo-HDL binding capacity. Similar binding sites for [125I]iodo-LDL and [125I]iodo-HDL were demonstrated in cells prepared from human placenta by trypsin digestion and maintained in monolayer culture.