Schütt Burkhardt Siegfried, Abbadi Amine, Loddenkötter Brigitte, Brummel Monika, Spener Friedrich
Institut für Biochemie, Universitat Munster, Wilhelm-Klemm-Str. 2, Germany.
Planta. 2002 Sep;215(5):847-54. doi: 10.1007/s00425-002-0803-8. Epub 2002 Jun 20.
With the aim of elucidating the mechanisms involved in the biosynthesis of medium-chain fatty acids in Cuphea lanceolata Ait., a crop accumulating up to 90% decanoic acid in seed triacylglycerols, cDNA clones of a beta-ketoacyl-acyl carrier protein (ACP) synthase IV (clKAS IV, EC 2.3.1.41) were isolated from C. lanceolata seed embryos. The amino acid sequence deduced from clKAS IV cDNA showed 80% identity to other plant KAS II-type enzymes, 55% identity towards plant KAS I and over 90% towards other Cuphea KAS IV-type sequences. Recombinant clKAS IV was functionally overexpressed in Escherichia coli, and substrate specificity of purified enzyme showed strong preference for elongation of short-chain and medium-chain acyl-ACPs (C4- to C10-ACP) with nearly equal activity. Further elongation steps were catalysed with distinctly less activity. Moreover, short- and medium-chain acyl-ACPs exerted a chain-length-specific and concentration-dependent substrate inhibition of clKAS IV. Based on these findings a regulatory mechanism for medium-chain fatty acid synthesis in C. lanceolata is presented.
为阐明披针叶萼距花（Cuphea lanceolata Ait.）中链脂肪酸生物合成所涉及的机制，从披针叶萼距花种子胚中分离出β-酮脂酰-酰基载体蛋白（ACP）合酶IV（clKAS IV，EC 2.3.1.41）的cDNA克隆。披针叶萼距花是一种在种子三酰甘油中积累高达90%癸酸的作物。从clKAS IV cDNA推导的氨基酸序列与其他植物KAS II型酶有80%的同一性，与植物KAS I有55%的同一性，与其他萼距花KAS IV型序列有超过90%的同一性。重组clKAS IV在大肠杆菌中实现了功能过表达，纯化酶的底物特异性显示出对短链和中链酰基-ACP（C4至C10-ACP）的延伸有强烈偏好，且活性几乎相等。进一步的延伸步骤催化活性明显较低。此外，短链和中链酰基-ACP对clKAS IV表现出链长特异性和浓度依赖性的底物抑制作用。基于这些发现，提出了披针叶萼距花中链脂肪酸合成的调控机制。
