ACETIC ACID OXIDATION BY ESCHERICHIA COLI: EVIDENCE FOR THE OCCURRENCE OF A TRICARBOXYLIC ACID CYCLE
ACETIC ACID OXIDATION BY ESCHERICHIA COLI: EVIDENCE FOR THE OCCURRENCE OF A TRICARBOXYLIC ACID CYCLE
复制标题
大肠杆菌的乙酸氧化：三羧酸循环发生的证据
作者：
H. Swim;L. Krampitz
三羧酸循环作为解释动物组织氧化乙酸的机制已得到普遍接受。细菌研究中获得的数据不满足动物组织循环所依据的许多标准（克雷布斯，1948-1949）。在前一份报告中，Saz和Krampitz（1954）批判性地评估了这个问题应用于细菌。本文叙述了在不加载体的情况下分离乙酸氧化中间体的技术。这些中间体彼此之间、与回收的乙酸盐之间以及与呼吸二氧化碳之间处于大致完全的同位素平衡。这些数据与使用Lydeikticu微球菌（Saz和Krampitz，1950; Ajl和Kamen，1950）和大肠杆菌（Swim和Krampitz，1950; Ajl和Kamen，1950）的载体实验获得的结果相反。在后一种情况下，来自乙酸-2-C4的同位素未在显著程度上掺入α-酮戊二酸。另一方面，载体琥珀酸具有高放射性，羧基碳与呼吸二氧化碳几乎完全处于同位素平衡。这些数据可以解释为三羧酸循环作为E.大肠杆菌中，并且主要机制涉及乙酸酯缩合为琥珀酸酯（Thunberg缩合）和二羧酸循环的其他反应。Saz和Krampitz（1954）已经证明，代谢α-酮戊二酸和作为载体添加的α-酮戊二酸之间的不平衡可以解释观察到的结果，因此，二羧酸循环的证据不令人满意。实验结果
The tricarboxylic acid cycle has received general acceptance as a mechanism to explain the oxidation of acetic acid by animal tissues. The data obtained in studies with bacteria do not satisfy many of the criteria on which the cycle was based in animal tissues (Krebs, 1948-1949). In the preceding report, Saz and Krampitz (1954) critically evaluated this problem as applied to bacteria. Techniques were described which permit the isolatioga of intermediates of acetate oxidation in the absence of added carriers. These intermediates were in approximately complete isotopic equilibrium with each other, with the recovered acetate, and with the respiratory carbon dioxide. These data were in contrast with the results obtained with carrier experiments employing Micrococcus lydeikticu (Saz and Krampitz, 1950; Ajl and Kamen, 1950) and Escherichia coli (Swim and Krampitz, 1950; Ajl and Kamen, 1950). In the latter case, isotope from acetate-2-C4 was not incorporated into a-ketoglutarate to a significant extent. The carrier succinate, on the other hand, was highly radioactive, and the carboxyl carbons were in almost complete isotopic equilibrium with the respiratory carbon dioxide. These data could be interpreted as evidence that the tricarboxylic acid cycle is of no quantitative importance as a mechani for the oxidation of acetate by E. coli and that the major mechanism involves acetate condensation to succinate (Thunberg condensation) and the other reactions of the dicarboxylic acid cycle. It has been shown by Saz and Krampitz (1954) that nonequilibration between metabolic a-ketoglutarate and that added as a carrier can account for the observed results, and, therefore, the evidence for the dicarboxylic acid cycle was unsatisfactory. The results of experiments