【摘要】 <正> 精氨酸酶广泛存在于生物界(Meister,1965)。在高等动物中,它是尿素循环中的重要环节(Ratner,1977)。关于昆虫界是否存在鸟氨酸循环问题一直未有定论(Candy,1965)。在尿素循环的几个环节中,Inokuchi等观察到一些个别的酶和代谢环节(Inokuchi等1969;Powles等1972),但仅仅根据这些材料推断尿素循环在昆虫体内的存在尚嫌证据更多还原

【Abstract】 Nutritional studies have indicated that insects, in general, are unable to synthesize arginine for their needs. In some insects this nutritional requirement can be replaced by citrulline, but not ornithine, and the evidence for the existence of the urea cycle in insects is scanty. In the fat body tissues of Bombyx mori and Philosama Cynthia ricini we have been unable to demonstrate the existence of either ornithine transcarbamylase or argininosuccinase. This suggests that, in general, insect can not synthesize arginine from ornithine by urea cycle.In the present paper it showed that arginase, ornithine-δ transaminase and side chain transaminases (valine, leucine, isoleuc-ine-glutamate transaminases) were detected in the fat body of Bombyx mori and Philosama cynthia ricini at different stages during the development. The activities of arginase and side chain transaminases were found to be the highest in the fat body of fifth instar larvae and adults and lowest in the embryo and pupae. The ornithine-δ transaminase was found to be highest in the fat body of the fifth instar larvae, but in constrast to the arginase and side chain transaminases, to be higher in the pupae.The tissue preparations of fat body have been shown to form orithine, urea, glutamic acid and proline at the expense of arginine and a-ketoglutaric acid. In the presence of boric acid less ornithine, urea, and proline were found, but ornithine-δ transaminase was not inhibited by boric acid. It was also demonstrated that the pathway from arginine to proline via ornithine with the formation of urea occurs in the fat body of the silkworm and the formation of proline at the expense of arginine and a-ketoglutarate are the results of three sequential enzymatic reactions, viz, arginase, ornithine-δ transaminase and pyrroline-5-carboxylate reductase.It was also shown that the larger amount of urea in the feces of Philosama cynthia ricini as compared witli Bombyx mori agreeswell with the higher activity of arginase in. Philosama cynthia ricini.The biochemical regulation of these eu/ymes has also been discussed.更多还原