Amino Acid Biosynthesis in the Spirochete Leptospira: Evidence for a Novel Pathway of Isoleucine Biosynthesis
Amino Acid Biosynthesis in the Spirochete Leptospira: Evidence for a Novel Pathway of Isoleucine Biosynthesis
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螺旋体钩端螺旋体中的氨基酸生物合成：异亮氨酸生物合成新途径的证据
作者：
N. Charon;R. C. Johnson;D. Peterson
将放射性二氧化碳与问号钩端螺旋体血清型semaranga和tarassovi的生长细胞一起孵育，并测定细胞氨基酸内标记的比活度和分布。发现除异亮氨酸外的所有酸稳定氨基酸的碳骨架的来源与这些氨基酸的已知生物合成途径一致。使用放射性二氧化碳和其他示踪剂的实验表明，大多数异亮氨酸是通过不涉及苏氨酸的途径合成的。通过这一途径，异亮氨酸的碳骨架由乙酰辅酶A的两个丙酮酸残基（碳2和3）和乙酸残基组成。同位素竞争研究表明该途径受异亮氨酸的调控。结果进行了讨论，涉及柠檬酸作为中间体的异亮氨酸生物合成的两个拟议的途径。
Radioactive carbon dioxide was incubated with growing cells of Leptospira interrogans serotypes semaranga and tarassovi, and the specific activities and distribution of the label within the cellular amino acids were determined. The origins of the carbon skeletons of all the acid-stable amino acids except isoleucine were found to be consistent with known biosynthetic pathways for these amino acids. Experiments using radioactive carbon dioxide and other tracers indicated that most of the isoleucine was synthesized by a pathway not involving threonine. The origin of the carbon skeleton of isoleucine consisted of two residues of pyruvate (carbons 2 and 3) and acetate of acetyl-coenzyme A by this pathway. Isotope competition studies indicated that the pathway was regulated by isoleucine. The results are discussed in relation to two proposed pathways of isoleucine biosynthesis involving citramalate as an intermediate.