caa a22 4500 47710116X CHVBK 20180405111541.0 cr unu---uuuuu 170330e19960201xx s 000 0 eng 10.1007/BF00206253 doi (NATIONALLICENCE)springer-10.1007/BF00206253 In-vitro evidence for feed-back regulation of β-ketoacyl-acyl carrier protein synthase III in medium-chain fatty acid biosynthesis [Elektronische Daten] [Fritzi Brück, Monika Brummel, Ricardo Schuch, Friedrich Spener] The cerulenin-insensitive β-ketoacyl-acyl carrier protein (ACP) synthase III (KAS III, EC 2.3.1.41) catalyzes the first condensing step of the fatty-acid synthase (FAS) reaction in plants and bacteria, using directly acetyl-CoA as substrate for condensation with malonyl-ACP. In order to identify a possible site for regulation of the biosynthesis of medium-chain fatty acids, the influence of acyl-ACPs of different chain-lengths (C4,C6,C8 and C10) on the activity of KAS III was investigated in vitro using an FAS preparation from seeds of Cuphea lanceolata Ait. (a crop accumulating up to 90% decanoic acid into triacylglycerols) that had been treated with 100 μM cerulenin. All acyl-ACPs investigated led to a decrease in the activity of KAS III towards acetyl-CoA, an effect apparently related to the length of the acyl chain. Analysis of the reaction products of the assay revealed that short-chain acyl-ACPs elongated to a very small extent simultaneously with acetyl-CoA. This extent of elongation did not correlate with the decrease in KAS III-activity levels. These data excluded the possibility of competition between acetyl-CoA and acyl-ACPs, but indicated that acyl-ACPs inhibited the enzyme. Decanoyl-ACP caused the highest decrease in enzyme activity (IC50 = 0.45 μM), thus being a potent inhibitor of KAS III. Michaelis-Menten kinetics revealed that the inhibition of KAS III by decanoyl-ACP was non-competitive in relation to malonyl-ACP and uncompetitive in relation to acetyl-CoA. Moreover, our data indicate that KAS III has a strict specificity for the elongation of acetyl-CoA. An inhibition of KAS III by acyl-ACPs was observed in experiments using FAS preparations from rape seeds and spinach leaves, but the inhibition of KAS III from C. lanceolata seeds by decanoyl-ACP was approximately 1.5-fold higher. The data provide evidence that acyl-ACPs are involved in the modulation of plant fatty-acid biosynthesis by a feed-back mechanism. Springer-Verlag, 1996 Cuphea nationallicence Fatty acid synthase nationallicence β-Ketoacyl-ACP synthase III (feed-back regulation) nationallicence Seed nationallicence ACP : acyl carrier protein nationallicence DTT : dithiothreitol nationallicence TCA : trichloroacetic acid nationallicence ecACP : acyl carrier protein from Escherichia coli nationallicence FAS : fatty-acid synthase nationallicence IC50 : concentration causing 50% inhibition nationallicence KAS : β-ketoacyl-ACP synthase nationallicence NEM : N-ethylmaleimide nationallicence Brück Fritzi Institut für Biochemie, Universität Münster, Wilhelm-Klemm-Strasse 2, D-48149, Münster, Germany aut Brummel Monika Institut für Biochemie, Universität Münster, Wilhelm-Klemm-Strasse 2, D-48149, Münster, Germany aut Schuch Ricardo Institut für Chemo- und Biosensorik, Mendelstrasse 7, D-48149, Münster, Germany aut Spener Friedrich Institut für Biochemie, Universität Münster, Wilhelm-Klemm-Strasse 2, D-48149, Münster, Germany aut Planta Springer-Verlag 198/2(1996-02-01), 271-278 0032-0935 198:2<271 1996 198 425 https://doi.org/10.1007/BF00206253 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00206253 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Brück Fritzi Institut für Biochemie, Universität Münster, Wilhelm-Klemm-Strasse 2, D-48149, Münster, Germany aut NATIONALLICENCE 700 1- Brummel Monika Institut für Biochemie, Universität Münster, Wilhelm-Klemm-Strasse 2, D-48149, Münster, Germany aut NATIONALLICENCE 700 1- Schuch Ricardo Institut für Chemo- und Biosensorik, Mendelstrasse 7, D-48149, Münster, Germany aut NATIONALLICENCE 700 1- Spener Friedrich Institut für Biochemie, Universität Münster, Wilhelm-Klemm-Strasse 2, D-48149, Münster, Germany aut NATIONALLICENCE 773 0- Planta Springer-Verlag 198/2(1996-02-01), 271-278 0032-0935 198:2<271 1996 198 425 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer