铵离子对梅岭霉素生物合成的调控效应

通过考察不同浓度的硫酸铵对梅岭霉素生物合成的影响，证实在低浓度下，硫酸铵可以促进梅岭霉素的生物合成，当其浓度大于5mmol/L时，菌丝生长和产物合成均受到抑制，而耗糖速率却随着铵离子的浓度增大而增大。在此基础上，进一步测定了与梅岭霉素生物合成和糖代谢过程密切相关的6种酶的活性变化，结果表明较高浓度的铵离子对6_磷酸葡萄糖脱氢酶、柠檬酸合成酶、琥珀酸脱氢酶以及脂肪酸合成酶的活性均表现出一定的促进作用，而对缬氨酸脱氢酶和甲基丙二酰CoA羧基转移酶的活性进行抑制，由此产生的结果一方面是HMP途径和TCA循环得到了加强，促进了菌体的初级代谢，另一方面则是梅岭霉素生物合成所需前体的来源受到限制，从而造成了梅岭霉素的低产。

Regulatory effects of ammonium ions on the biosynthesis of meilingmycin

Based on the effects of different ammonium sulfate concentrations on meilingmycin biosynthesis, the results show that lower concentration of ammonium ions stimulates the biosynthesis of meilingmycin, while the concentration of higher than 5mmol/L inhibits the mycelial growth and the biosynthesis of the products. However, the sugar consumption rate increases with the elevating concentration of ammonium sulfate. On this basis, six enzymes, which are greatly related to the meilingmycin biosynthesis and the glucose metabolism, were measured and analyzed during the meilingmycin fermentation process. The results suggest that glucose_6_phosphate dehydrogenase, citrate synthase, succinate dehydrogenase and fatty acid synthase are stimulated by higher concentration of ammonium ions, while valine dehydrogenase and methylmalonyl_CoA carboxyltransferase are inhibited. From the results it follows that ammonium ions favors primary metabolism, that is, the HMP passway and the TCA circle is enhanced, as well as the source of the precursors for the biosynthesis of meilingmycin is restricted, which bring about the lower production of meilingmycin.