The Biochemistry of Lipophorin: Lipophorin and Adipokinetic hormone

该研究项目的主要目的是阐明蝗虫等昆虫长时间飞行的分子机制。我们以前发现，当昆虫脂肪运动激素（AKH）注射到成年蝗虫时，脂肪体中的载脂蛋白负载甘油二酯在很大程度上受到刺激，这导致载脂蛋白密度急剧下降，并显着增加载脂蛋白颗粒的大小。除了这些变化之外，AKH注射引起低分子量载脂蛋白、载脂蛋白-III（apo-III）与载脂蛋白的缔合。AKH引起的脂转运蛋白的变化可能是促进了作为燃料的甘油二酯向飞行肌的供应，为了进一步阐明AKH的作用机制，有必要建立一个体外系统，使AKH在体内观察到的上述作用在体外完全得到证实。我们最近建立了一个重构的孵育体系，其中纯化的Lipophorin和apo-III与分离的脂肪体在AKH存在下在持续过量的氧气供应下孵育。我们使用该系统证明了1）AKH的作用需要钙离子，2）AKH的完全作用需要每摩尔载脂蛋白添加9摩尔apo-III，3）AKH的作用是全有或全无，4）apo-III的存在对于AKH的作用是必不可少的，和5）由载脂蛋白装载的二酰基甘油的量取决于载脂蛋白的量。该系统的建立为进一步研究apo-III的生理功能奠定了基础。

The major purpose of this research project is to elucidate the molecular mechanism of a long flight in insects such as locusts. We have previously found that when insect adipokinetic hormone (AKH) is injected to adult locusts, the loading of diacylglycerol by lipophorin from the fat body is stimulated to a large extent, which results in the dramatical shift of lipophorin density to a lower value and significant increase in size of lipophorin particles. In addition to these changes, the AKH injection causes the association of a low molecular weight apoprotein, apolipophorin-III (apo-III) with lipophorin. These changes in lipophorin induced by AKH seems to facilitate the supply of diacylglycerol as fuel to flight muscle.In order to further elucidate the mechanism of AKH action, it is essntial to establish the in vitro system, in which the above mentioned action of AKH observed in vivo can entirely be demonstrated in vitro. We have recently achieved to establish the reconstracted incubation system in which the purified lipophorin and apo-III are incubated with the isolated fat body in the presence of AKH under the contineous supply of excess oxygen. We demonstrated using this system that 1) the action of AKH requires calcium ion, 2) the full action of AKH requires the addition of 9 moles apo-III per each mole lipophorin, 3) the action of AKH is all or nothing, 4) the presence of apo-III is essential for the action of AKH, and 5) the amount of diacylglycerol loaded by lipophorin depends on the amount of apo-III added.The establishemnt of the reconstracted system seems to greatly facilitate to develop this research field including the elucidaton of physiological role of apo-III.