Milner N P, Rees H H
Biochem J. 1985 Oct 15;231(2):369-74. doi: 10.1042/bj2310369.
The epimerization of ecdysone to 3-epiecdysone has been investigated in a dialysed cytosolic enzyme preparation from midgut of sixth instar Spodoptera littoralis larvae, with particular emphasis on establishing the intermediacy of 3-dehydroecdysone. Incubation of ecdysone with the dialysed cytosolic preparation furnished 3-dehydroecdysone as the only detectable product, the reaction being oxygen-dependent. The enzyme preparation catalysed reduction of 3-dehydroecdysone to 3-epiecdysone and ecdysone in the presence of NADH or NADPH. Whereas formation of 3-epiecdysone greatly predominated over that of ecdysone in the presence of NADPH, the converse applied when the cofactor was NADH. 3-Epiecdysone incubated with the enzyme preparation in the presence of various cofactors was not metabolized, indicating the irreversibility of the reduction of 3-dehydroecdysone to 3-epiecdysone and, hence, of the 3-epimerization process. The foregoing results, together with comparison of the metabolism of 3-dehydro[3H]ecdysone and [3H]ecdysone by the enzyme preparation in the presence of unlabelled ecdysone and NADPH, support the intermediacy of 3-dehydroecdysone in the 3-epimerization of ecdysone.
在对六龄期海滨夜蛾幼虫中肠的透析胞质酶制剂进行的研究中，已对蜕皮激素向3-表蜕皮激素的差向异构化进行了调查，特别着重于确定3-脱氢蜕皮激素作为中间产物的情况。将蜕皮激素与透析后的胞质制剂一起温育，结果表明仅可检测到3-脱氢蜕皮激素这一产物，该反应依赖于氧气。在存在NADH或NADPH的情况下，该酶制剂可催化3-脱氢蜕皮激素还原为3-表蜕皮激素和蜕皮激素。在存在NADPH时，3-表蜕皮激素的形成比蜕皮激素的形成占主导地位得多，而当辅因子为NADH时情况则相反。在存在各种辅因子的情况下，将3-表蜕皮激素与酶制剂一起温育时不会发生代谢，这表明3-脱氢蜕皮激素还原为3-表蜕皮激素以及因此的3-差向异构化过程是不可逆的。上述结果，连同在未标记的蜕皮激素和NADPH存在下，该酶制剂对3-脱氢[3H]蜕皮激素和[3H]蜕皮激素代谢情况的比较，均支持3-脱氢蜕皮激素在蜕皮激素3-差向异构化过程中作为中间产物的情况。
