Characterization of ADP-glucose transport across the cereal endosperm amyloplast envelope

被引:46
作者
Bowsher, Caroline G.
Scrase-Field, Edward F. A. L.
Esposito, Sergio
Emes, Michael J.
Tetlow, Ian J. [1 ]
机构
[1] Univ Guelph, Dept Mol & Cellular Biol, Coll Biol Sci, Guelph, ON N1G 2W1, Canada
[2] Univ Manchester, Fac Life Sci, Manchester M13 9PT, Lancs, England
[3] Univ Naples Federico II, Dipartimento Biol Vegetale, I-80139 Naples, Italy
基金
英国生物技术与生命科学研究理事会;
关键词
ADP-glucose transport; amylopectin; amyloplasts; amylose; starch synthesis;
D O I
10.1093/jxb/erl297
中图分类号
Q94 [植物学];
学科分类号
071001 ;
摘要
Most of the carbon used for starch biosynthesis in cereal endosperms is derived from ADP-glucose (ADP-Glc) synthesized by extra-plastidial AGPase activity, and imported directly across the amyloplast envelope. The properties of the wheat endosperm amyloplast ADP-Glc transporter were analysed with respect to substrate kinetics and specificities using reconstituted amyloplast envelope proteins in a proteoliposome-based assay system, as well as with isolated intact organelles. Experiments with liposomes showed that ADP-Glc transport was dependent on counter-exchange with other adenylates. Rates of ADP-Glc transport were highest with ADP and AMP as counter-exchange substrates, and kinetic analysis revealed that the transport system has a similar affinity for ADP and AMP. Measurement of ADP and AMP efflux from intact amyloplasts showed that, under conditions of ADP-Glc-dependent starch biosynthesis, ADP is exported from the plastid at a rate equal to that of ADP-Glc utilization by starch synthases. Photo-affinity labelling of amyloplast membranes with the substrate analogue 8-azido-[alpha-P-32]ADP-Glc showed that the polypeptide involved in substrate binding is an integral membrane protein of 38 kDa. This study shows that the ADP-Glc transporter in cereal endosperm amyloplasts imports ADP-Glc in exchange for ADP which is produced as a by-product of the starch synthase reaction inside the plastid.
引用
收藏
页码:1321 / 1332
页数:12
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