The Biochemistry of Lipophorin: Lipophorin and Adipokinetic hormone

这项研究的主要目的是阐明蝗虫等昆虫长时间飞行的分子机制。我们先前发现，当昆虫脂肪运动激素(AKH)注射到成虫体内时，很大程度上刺激了脂蛋白从脂肪体中负载二酰甘油，导致脂蛋白密度急剧向低值移动，脂蛋白颗粒明显增大。除了这些变化外，AKH注射还导致一种低分子载脂蛋白-III(apo-III)与脂蛋白结合。AKH引起的脂蛋白的这些变化似乎促进了二酰甘油作为燃料供应给飞行肌肉。为了进一步阐明AKH的作用机制，有必要建立能够在体外完全证明AKH在体内观察到的上述作用的体外系统。我们最近成功地建立了重组孵育体系，在这个体系中，纯化的脂蛋白和apo-III与分离的脂肪体在AKH存在下，在持续的过量氧气供应下孵育。我们用这个系统证明：1)AKH的作用需要钙离子，2)AKH的充分作用需要每个摩尔脂蛋白增加9个摩尔apo-III，3)AKH的作用要么全有要么没有，4)apo-III的存在对AKH的作用是必不可少的，5)脂蛋白负载的二酰甘油量取决于apo-III的加入量。重组系统的建立似乎极大地促进了这一研究领域的发展，包括apo-III生理作用的阐明。

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.