Developmental control of amino acid metabolism in the silkworm, Bombyx mori

1.通过测定桑蚕体脂肪组织精氨酸酶活性，探讨了饲喂人工桑叶的桑蚕血淋巴中尿素浓度比饲喂新鲜桑叶的桑蚕高2倍的原因。利用五龄幼虫的组织，研究了脂肪体精氨酸酶的测定条件。用人工饲料饲养和新鲜桑叶饲养，测定了从5龄幼虫开始至成虫出蛹前1天的脂体精氨酸酶活性。两种饲料饲养的家蚕活性变化相似，在5龄中期达到峰值。用人工饲料饲养的家蚕，其每虫活性比用新鲜桑叶饲养的家蚕高2倍。在人工饲料和新鲜桑叶饲养的幼虫中，每毫克脂肪体蛋白的Argianse活性表现出相似的变化。人工饲料饲养的幼虫每虫蛋白质含量较高。这些结果表明，脂肪体在摄入人工饮食后合成的蛋白质中含有精氨酸酶。亚细胞定位研究表明，家蚕幼虫脂肪体精氨酸酶定位于线粒体基质中。这一结果与普遍认为精氨酸酶定位于细胞的观点相反。线粒体基质中的氨气动物精氨酸。线粒体内膜中尿酸动物精氨酸酶。细胞质中致尿动物精氨酸酶。进一步的研究将揭开谜底。

1.The reason why two fold higher urea concentrations in the haemolymph in the silkworm larvae reared on an artificial diet result than those reared on fresh mulberry leaves was investigated by measuring arginase activity in the fat body tissue.2.Assay conditions for arginase in the fat body was studied using the tissues from the fifth instar larvae.3.Fat body arginase activity was measured from the beginning of the fifth instar larvae until the pupae at one day before adult emergence using insects reared on an artigicial diet and on fresh mulberry leaves.Silkworms reared on either diet showed similar activity changes with a peak at the middle of the fifth instar larvae. Silkworms reared on an artificial diet showed two fold higher activity per individual insect basis than those reared on fresh mulberry leaves.5.Argianse activity per mg fat body protein showed similar changes in the level both in the larvae reared on an artificial diet and on fresh mulberry leaves. Protein content per individual insect basis was higher in the larvae reared on an artificial diet. These results suggest that proteins synthesized in the fat body in response to intake of an artificial diet involves arginase in it.6.Subcellular localization studies indicated that arginase of silkworm larval fat body localized in mitochondrial matrix. This result was in contrast to the widespread belief of arginase localization in cells. Ammonotelic animal arginse in the mitochondrial matrix. Uricotelic animal arginase in mitochondrial innnermembrane. Ureotelic animal arginase in cytosol. Further studies should unveil the mystery.