ACETOHYDROXY ACID SYNTHASE ACTIVITY IN CHLORELLA-EMERSONII UNDER AUTOTROPHIC AND HETEROTROPHIC GROWTH-CONDITIONS
ACETOHYDROXY ACID SYNTHASE ACTIVITY IN CHLORELLA-EMERSONII UNDER AUTOTROPHIC AND HETEROTROPHIC GROWTH-CONDITIONS
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DOI：
10.1104/pp.94.2.614
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发表时间：
1990-10-01
期刊：
影响因子：
7.4
通讯作者：
BARAK, Z
中科院分区：
文献类型：
--
作者：
LANDSTEIN, D;CHIPMAN, DM;BARAK, Z
研究了绿色单细胞小球藻的乙酰羟酸合成酶(AHAS)活性。比较了在黑暗中自养和异养生长的藻类在葡萄糖上的这种活性及其调节。没有发现存在一种以上酶的证据。异养和自养细胞的粗提物对丙酮酸的Km为9毫摩尔，2-酮丁酸酯作为第二底物的Km值是丙酮酸的22倍，0.5毫摩尔的Valine抑制50%，0.3微摩尔的磺脲(SMM)抑制50%。分离到抗SMM的自发突变体，可能是含有抗SMM AHAs活性的单基因突变体。因此，AHAs似乎是默氏梭菌中SMM的唯一直接靶点。突变体在自养和异养条件下对SMM的抗性相当，这一事实进一步支持了相同的酶在两种生理条件下发挥作用的结论。缬氨酸和异亮氨酸的加入部分解除了SMM对生物量增加的抑制，但不能部分解除SMM对细胞分裂的抑制。
Acetohydroxyacid synthase (AHAS) activity was studied in the green unicellular alga Chlorella emersonii. This activity and its regulation was compared in the algae grown autotrophically and heterotrophically on glucose in the dark. No evidence for the existence of more than one enzyme was found. The activity in crude extracts from either heterotrophically or autotrophically grown cells showed a Km for pyruvate of 9 millimolar, a 22-fold preference for 2-ketobutyrate over pyruvate as the second substrate, 50% inhibition by 0.5 millimolar valine, and 50% inhibition by 0.3 micromolar sulfometuron methyl (SMM). Spontaneous mutants of the alga resistant to SMM were isolated, which appeared to be single gene mutants containing SMM-resistant AHAS activity. Hence, AHAS appears to be the sole direct target site of SMM in C. emersonii. The fact that the mutants had equivalent SMM resistance under auto- and heterotrophic conditions further supports the conclusion that the same enzyme functions under both physiological regimes. The addition of valine and isoeleucine leads to partial relief of SMM inhibition of biomass increase, but not of SMM inhibition of cell division.