RICINOLEIC ACID BIOSYNTHESIS AND TRIACYLGLYCEROL ASSEMBLY IN MICROSOMAL PREPARATIONS FROM DEVELOPING CASTOR-BEAN (RICINUS-COMMUNIS) ENDOSPERM
RICINOLEIC ACID BIOSYNTHESIS AND TRIACYLGLYCEROL ASSEMBLY IN MICROSOMAL PREPARATIONS FROM DEVELOPING CASTOR-BEAN (RICINUS-COMMUNIS) ENDOSPERM
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DOI：
10.1042/bj2800507
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发表时间：
1991-12-01
影响因子：
4.1
通讯作者：
STYMNE, S
中科院分区：
文献类型：
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作者：
BAFOR, M;SMITH, MA;STYMNE, S
从蓖麻子（Ricinus communis）发育胚乳的微粒体膜制剂催化油酸从[C-14]油酰辅酶A转移到磷脂酰胆碱（PtdCho）。在存在NADH的情况下，从[C-14]油酸酯合成放射性蓖麻油酸酯（12-羟基十八碳-9-烯酸酯），并且这在PtdCho中以游离脂肪酸的形式大量回收。向这些孵育混合物中添加未标记的蓖麻油酰-CoA既没有增加酰基-CoA级分中发现的低[C-14]蓖麻油酸酯浓度，也没有降低PtdCho和游离脂肪酸中的[C-14]蓖麻油酸酯浓度，因此没有获得油酰-CoA作为底物进行羟基化的证据。添加NADH，必要的蓖麻油酸的形成，导致PtdCho中的总放射性的减少与相应的增加在游离蓖麻油酸中的标记量。这种增加是由于磷脂酶A的作用，其从PtdCho释放蓖麻油酸但不释放油酸。这种磷脂酶活性，攻击蓖麻油酰-PtdCho，但不油酰-PtdCho，也证明了微粒体制剂从发展中的子叶的红花和油菜。蓖麻子微粒体PtdCho中不同位置的酰基分析表明，蓖麻油酸酯几乎完全与位置sn-2相关。同样，在与含有NADH和[C-14]油酰辅酶A的微粒体制备物孵育后，[C-14]PtdCho中形成的[C-14]蓖麻油酸酯位于位置sn-2，位置sn-1无。相反，通过[C-14]油酰基-PtdCho去饱和形成的[C-14]亚油酸酯存在于两个位置。在ATP、CoA和Mg 2+存在下，PtdCho释放的蓖麻油酸被活化为蓖麻油酰-CoA。蓖麻油酰辅酶A是3-磷酸甘油（Gro 3 P）酰化产生磷脂酸和三酰甘油的有效酰基供体。在存在Gro 3 P的情况下，用[C-14]油酰-CoA和[C-14]蓖麻油酰-CoA的等摩尔混合物孵育的微粒体制备物中，仅少量[C-14]蓖麻油酸酯进入PtdCho，并且认为这是通过二酰基甘油池和PtdCho之间的磷酸胆碱基团交换。根据我们的研究结果，蓖麻油酸酯的形成和其纳入三酰甘油在蓖麻豆胚乳的计划提出。
Microsomal membrane preparations from the developing endosperm of castor bean (Ricinus communis) catalysed the transfer of oleate from [C-14]oleoyl-CoA to phosphatidylcholine (PtdCho). In the presence of NADH, radioactive ricinoleate (12-hydroxyoctadec-9-enoate) was synthesized from [C-14]oleate, and this was largely recovered in PtdCho and as free fatty acid. The addition of unlabelled ricinoleoyl-CoA to these incubation mixtures did not increase the low [C-14]ricinoleate concentration found in the acyl-CoA fraction nor decrease the [C-14]ricinoleate concentration in PtdCho and free fatty acid, and thus no evidence was obtained for a hydroxylation with oleoyl-CoA as a substrate. The addition of NADH, necessary for the formation of ricinoleate, caused a decrease of the total radioactivity in PtdCho with a corresponding increase in the amount of label in free ricinoleic acid. This increase was due to the action of a phospholipase A, which released ricinoleic acid but not oleic acid from PtdCho. Such a phospholipase activity, attacking ricinoleoyl-PtdCho but not oleoyl-PtdCho, was also demonstrated in microsomal preparations from developing cotyledons of safflower and oil-seed rape. An analysis of the acyl groups at different positions in microsomal PtdCho of castor bean showed that ricinoleate was almost entirely associated with position sn-2. Likewise the [C-14]ricinoleate in [C-14]PtdCho formed after incubations with microsomal preparations with NADH and [C-14]oleoyl-CoA resided in position sn-2 with none in position sn-1. In contrast, the [C-14]linoleate formed by desaturation of [C-14]oleoyl-PtdCho was present at both positions. In the presence of ATP, CoA and Mg2+, the ricinoleate acid released from PtdCho was activated to ricinoleoyl-CoA. The ricinoleoyl-CoA was an efficient acyl donor in the acylation of glycerol 3-phosphate (Gro3P) to yield phosphatidic acid and triacylglycerols. In microsomal preparations incubated with an equimolar mixture of [C-14]oleoyl-CoA and [C-14]ricinoleoyl-CoA in the presence of Gro3P, only a minor amount of [C-14]ricinoleate entered PtdCho, and this was believed to be via the exchange of phosphocholine groups between a diacylglycerol pool and the PtdCho. On the basis of our results, a scheme of ricinoleate formation and its incorporation into triacylglycerols in castor-bean endosperm is proposed.