Shimizu S, Dempsey W B
J Bacteriol. 1978 Jun;134(3):944-9. doi: 10.1128/jb.134.3.944-949.1978.
Escherichia coli K-12 mutants with serC genotype required pyridoxine and serine for normal growth, as do E. coli B mutants of this type. Mutants of the K-12 strain, however, reverted easily to pyridoxine independence without regaining activity in the 3-phosphoserine oxoglutarate transaminase coded for by the serC gene. Both these revertants and the parental type synthesized pyridoxine in normal amounts when 3-hydroxypyruvate was used as a supplement, although neither of these mutants could use this compound to satisfy their serine requirement. Since serine alone was inadequate to provide the nutritional requirement of serC mutants, these mutants must have been unable to synthesize 3-hydroxypyruvate from serine. We suggest that 3-phosphoserine oxoglutarate transaminase in normal E. coli serves as a catalyst for transaminating small amounts of serine to 3-hydroxypyruvate, which is then used in pyridoxine biosynthesis. In serC mutants, this activity is blocked, and these mutants then show a double requirement for serine and pyridoxine.
具有serC基因型的大肠杆菌K - 12突变体正常生长需要吡哆醇和丝氨酸,这种类型的大肠杆菌B突变体也是如此。然而,K - 12菌株的突变体很容易回复到对吡哆醇不依赖的状态,而serC基因编码的3 - 磷酸丝氨酸酮戊二酸转氨酶却没有恢复活性。当使用3 - 羟基丙酮酸作为补充剂时,这些回复突变体和亲本类型都能正常合成吡哆醇,尽管这些突变体都不能利用这种化合物来满足其丝氨酸需求。由于仅丝氨酸不足以满足serC突变体的营养需求,这些突变体一定无法从丝氨酸合成3 - 羟基丙酮酸。我们认为,正常大肠杆菌中的3 - 磷酸丝氨酸酮戊二酸转氨酶作为一种催化剂,将少量丝氨酸转氨生成3 - 羟基丙酮酸,然后用于吡哆醇的生物合成。在serC突变体中,这种活性被阻断,这些突变体随后表现出对丝氨酸和吡哆醇的双重需求。