Thimann Laboratories, University of California, Santa Cruz, California 95064.
Plant Physiol. 1978 Aug;62(2):173-8. doi: 10.1104/pp.62.2.173.
Enzyme assays on organelles isolated from the endosperm of germinating castor bean (Ricinus communis) by sucrose density gradient centrifugation showed that fatty acid synthesis from [(14)C]malonyl-CoA was localized exclusively in the plastids. The optimum pH was 7.7 and the products was mainly free palmitic and oleic acids. Both NADH and NADPH were required as reductants for maximum activity. Acetyl-CoA, and acyl-carrier protein from Escherichia coli increased the rate of fatty acid synthesis, while low O(2) levels suppressed synthesis. In the absence of NADPH or at low O(2) concentration, stearic acid became a major product at the expense of oleic acid. Fatty acid synthesis activity was highest during the first 3 days of germination, preceding the maximum development of mitochondria and glyoxysomes. It is proposed that the plastids are the source of fatty acids incorporated into the membranes of developing organelles.
采用蔗糖密度梯度离心法从萌发的蓖麻（Ricinus communis）胚乳中分离得到的细胞器的酶活性测定表明，从 [(14)C]丙二酰辅酶 A 合成脂肪酸仅定位于质体中。最适 pH 值为 7.7，产物主要是游离的棕榈酸和油酸。NADH 和 NADPH 均为最大活性所需的还原剂。乙酰辅酶 A 和来自大肠杆菌的酰基载体蛋白均能提高脂肪酸合成的速率，而低 O(2)水平则抑制合成。在没有 NADPH 或在低 O(2)浓度下，硬脂酸成为主要产物，而油酸的产量减少。脂肪酸合成活性在萌发的头 3 天最高，此时线粒体和乙醛酸体的发育达到最大值之前。因此，提出质体是合成的脂肪酸被整合到发育中的细胞器膜中的来源。
