Tobe S S, Pratt G E
Biochem J. 1974 Oct;144(1):107-13. doi: 10.1042/bj1440107.
The rate at which isolated corpora allata of adult female Schistocerca gregaria incorporate [(3)H]farnesenic acid and [(14)C]methionine into C(16)juvenile hormone in vitro was examined at different concentrations of farnesenic acid, methionine, O(2) and H(+) ions. Maximum juvenile hormone biosynthesis is obtained at a farnesenic acid concentration of 20mum. The range of optimum l-methionine concentrations (0.1-0.4mm) encompasses the physiological concentration of this substrate in the haemolymph. Hormone biosynthesis is dependent on O(2), but is not stimulated by hyperbaric oxygen tension. The glands had a maximum synthetic activity at pH8.0, but their activity was more reproducible in the the physiological range pH7.0-7.5. At pH6.5 and less, the synthetic ability was considerably decreased. The relative incorporations of the labelled substrates into methyl farnesoate and C(16) juvenile hormone indicate that [(3)H]farnesenic acid comes into isotopic equilibrium within the gland more rapidly than [(14)C]methionine. The incorporations into methyl farnesoate become stoicheiometric after 20min incubation and into C(16) juvenile hormone after a further 10min. Labelled juvenile hormone is detectable after 10min incubation and the rate of incorporation is constant for up to 4h. It is proposed that the described method may be usefully employed to assess the physiological changes in the enzymic competence of the glands to effect the last two stages in C(16) juvenile hormone biosynthesis.
在不同浓度的法尼烯酸、甲硫氨酸、氧气和氢离子条件下，研究了成年雌性沙漠蝗孤立咽侧体在体外将[（3）H]法尼烯酸和[（14）C]甲硫氨酸掺入C16保幼激素的速率。在法尼烯酸浓度为20μm时可获得最大保幼激素生物合成量。最佳L-甲硫氨酸浓度范围（0.1-0.4mm）涵盖了该底物在血淋巴中的生理浓度。激素生物合成依赖于氧气，但不受高压氧张力刺激。腺体在pH8.0时具有最大合成活性，但其活性在生理范围pH7.0-7.5内更具重复性。在pH6.5及更低时，合成能力显著下降。标记底物掺入法尼醇甲酯和C16保幼激素的相对掺入量表明，[（3）H]法尼烯酸在腺体内比[（14）C]甲硫氨酸更快达到同位素平衡。孵育20分钟后掺入法尼醇甲酯的量达到化学计量，再经过10分钟后掺入C16保幼激素。孵育10分钟后可检测到标记的保幼激素，掺入速率在长达4小时内保持恒定。有人提出，所描述的方法可有效地用于评估腺体在C16保幼激素生物合成的最后两个阶段中酶活性的生理变化。
