MODIFIED BRANCHED-CHAIN AMINO-ACID PATHWAYS GIVE RISE TO ACYL ACIDS OF SUCROSE ESTERS EXUDED FROM TOBACCO LEAF TRICHOMES
MODIFIED BRANCHED-CHAIN AMINO-ACID PATHWAYS GIVE RISE TO ACYL ACIDS OF SUCROSE ESTERS EXUDED FROM TOBACCO LEAF TRICHOMES
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DOI：
10.1111/j.1432-1033.1990.tb15415.x
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发表时间：
1990-03-10
期刊：
影响因子：
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通讯作者：
WAGNER, GJ
中科院分区：
文献类型：
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作者：
KANDRA, L;SEVERSON, R;WAGNER, GJ
来自支链氨基酸生物合成/催化剂的碳的主要转移以形成蔗糖酯的酰基部分（6-O-乙酰基-2，3，4-三-O-酰基-α- D-吡喃葡萄糖基-β- D-呋喃果糖苷）与分泌大量蔗糖酯的特化毛状体头细胞有关。烟草的表面化学与乙酰基和酰基取代基（T.I. 1068）蔗糖酯通过气相色谱/质谱法鉴定和定量。蔗糖酯是主要的表面组分，3-甲基戊酸、2-和3-甲基丁酸和甲基丙酸分别占总C3-C7酰基取代基的60%、25%和9%。放射性标记的苏氨酸，异亮氨酸，瓦尔，亮氨酸，丙酮酸和天冬氨酸，支链氨基酸途径的代谢产物，进行了比较与放射性标记的乙酸酯和蔗糖作为碳的供体蔗糖，乙酰基和酰基成分的蔗糖酯使用表皮与未受干扰的毛状体。还检查了具有生物合成能力的毛状体头部（蔗糖酯形成的位点）的制备。结果表明，3-甲基戊酰基和2-甲基丁酰基来源于支链氨基酸代谢的Thr途径，3-甲基丁酰基和甲基丙酰基通过丙酮酸途径形成，乙酰基主要通过乙酰辅酶A直接形成。提出的论点排除了参与脂肪酸合成酶的形成突出的酰基酸。结果表明，碳的分流远离生物合成的瓦尔，Leu和Ile可能是由于低水平的氨基酸利用蛋白质合成中专门的腺毛状体的腺头细胞。这将导致相应的含氧酸可用于CoA活化和酯化以形成蔗糖酯。初步的证据被发现参与的循环反应中的含氧酸链延长和利用的反丁烯二酸衍生的2-氧丁酸酯形成直链酰基取代基。
A major diversion of carbon from branched-chain amino acid biosynthesis/catabolism to form acyl moieties of sucrose esters (6-O-acetyl-2,3,4-tri-O-acyl-.alpha.-d-glucopyranosyl-.beta.-d-fructofuranosides) was observed to be associated with specialized trichome head cells which secrete large amounts of sucrose esters. Surface chemistry and acetyl and acyl substituent groups of tobacco (T.I. 1068) sucrose esters were identified and quantified by gas chromatography/mass spectrometry. Sucrose esters were prominent surface constituents and 3-methylvaleric acid, 2- and 3-methylbutyric acid, and methylpropionic acid accounted for 60%, 25% and 9%, respectively, of total C3-C7 acyl substituents. Radiolabeled Thr, Ile, Val, Leu, pyruvate and Asp, metabolites of branched-chain amino acid pathways, were compared with radioactively labeled acetate and sucrose as donors of carbon to sucrose, acetyl and acyl components of sucrose esters using epidermal peels with undisturbed trichomes. Preparations of biosynthetically competent trichome heads (site of sucrose esters formation) were also examined. Results indicate that 3-methylvaleryl and 2-methylbutyryl groups are derived from the Thr pathway of branched-chain amino acid metabolism, 3-methylbutyryl and methylpropionyl groups are formed via the pyruvate pathway, and that acetyl groups are principally formed directly via acetyl-CoA. Arguments are presented which rule out participation of fatty acid synthase in the formation of prominent acyl acids. Results suggest that the shunting of carbon away from the biosynthesis of Val, Leu and Ile may be due to a low level of amino acid utilization in protein synthesis in specialized glandular head cells of trichomes. This would result in the availability of corresponding oxo acids for CoA activation and esterification to form sucrose esters. Preliminary evidence was found for the involvement of cycling reactions in oxo-acid-chain lengthening and for utilization of pyruvate-derived 2-oxybutyrate to form straight-chain acyl substituents.