铵离子抑制a—vermectin生物合成的机理

实验中发现铵离子（NH4^ )对avermectin 的生物合成具有强烈的抑制作用，并对其机理进行了研究，。结果表明：铵离子对avermectin生物合成的抑制作用是通过同时作用于avermectin产生菌（Streptomyces avermitilis)糖代谢过程中的多个位点而实验的，发酵培养基中含有的少量铵离子，造成了avermectin链霉菌胞外淀粉酶的总活力降低；发酵液中的丙酮酸积累量明显降低。菌丝体内葡萄糖－6－磷酸脱氢酶活力降低；琥珀酸脱氢酶活力显著提高，最终造成了糖代谢过程中产生的可用于avermectin生物合成的短链脂肪酸数量减少，进而抑制抗生素的生物合成。

Mechanism of ammonia ion restraining the avermectin biosynthesis

It was found that the ammonia ion could distinctly inhibit the biosynthesis of avermectin and the mechanism of this phenomenon was investigated. The result indicated that several segments of carbohydrate metabolism in Streptomyces avermitilis were inhibited by ammonia ion. With small amount of ammonia ion added into fermentation culture medium, the total activity of diastase of Streptomyces avermitilis reduced and the accumulated quantity of pyruvate in the fermentation broth evidently dropped, at the same time, the energy of glucose 6 phosphate dehydrogenase (G6PD) in mycelium was decreased while the activity of succinate dehydrogenase was significantly increased. All of these result in the amount of short chain fatty acid from carbohydrate metabolism which could be used to synthesize avermectin to be reduced, consequently the biosynthesis of avermectin was inhibited.