| Research Abstract |
The major results are summarized as follows :
1. The primary action of adipokinetic hormone (AKH) is to stimulate the influx of extracellular calcium ion into the fat body cells which results in the activation of lipase via calcium-dependent protein kinase. Consequently, the formation of diacylglycerol from triacylglycerol is accelefated, which, in turn, promotes loading of diacyllgycerol by lipophporin from the fat body.
2. Low density lipophorin (LDLp) induced by AKH associates a different number of apolipophorin-III (apo-III), 7moles/ lipophorin to 14 moles/lipophorin, in accordance with the amount of diacylglycerol loaded by lipophorin, and most of LDLp contain about 9 moles apo-III per each mole of lipophorin. In addition, It was confirmed that the heterogeneity in size of LDLp particles previously observed is undoubtedly due to the intermolecular fusion of LDLp particles primarily formed by the action of AKH.
3. The insect blood sugar, trehalose, inhibits the loading of diacylglycerol by lipophorin from the fat body. This inhibition occurs at the physiological concentration of trehalose, about 60-80 mM ; however, at the commencement of long distance flight, the trehalose level sharply drops to 20 mM during the first 30 min, at which concentration no more inhibition takes place. This suggests that trehalose may play a dual function, i. e., serving as fuel and as a regulator in lipid transport.
4. Locust (as an insect having capacity of long distance flight) and cockroach (as an insect lacking the capacity) are compared. It was found that cockroach hemolymph lacks apolipophorin-III, and that cockroach fat body contains extremely small amount of diacylglycerol, which is equivalent to only one tenth of diacylglycerol content in locust fat body.
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