Formate fixation in pyruvate by Escherichia coli.

The phosphoroclastic decomposition of pyruvic acid to acetic and formic acids by enzyme extracts of Escherichia coli has been an object of study ever since acetyl phosphate was tentatively identified as an intermediate of this reaction (1). The finding by Utter, Lipmann, and Werkman that isotopic carbon of formate was incorporated into the carboxyl group and that the carboxyl carbon of acetate was converted to the carbonyl group of pyruvate was considered to support the postulate that the reaction was reversible (2, 3). Further evidence was obtained by Lipmann and Tuttle (4) who reported a synthesis of pyruvate from acetyl phosphate and formate and also by Kaplan and Lipmann (5) who observed that pyruvic acid was formed by incubating acetate, adenosinetriphosphate (ATP), and formate with dried cell suspensions of E. co&. However, when Strecker, Wood, and Krampitz (6) tested synthetic carboxyl-labeled acetyl phosphate with pyruvate and labeled formate, the residual pyruvate was found to contain isotopic carbon only in the carboxyl group derived from formate. Furthermore, when a labeled compound with properties similar to those of acetyl phosphate was produced from carbonyl-labeled pyruvate, it was found that neither this biologically formed compound nor any of the other possibly unknown end-products of pyruvate metabolism, except formate, exchanged carbon with newly added pyruvate (6). An attempt was made (6) to rationalize these results by postulating two hypotheses. In the first of these it was suggested that formic acid carbon was fixed in pyruvate by combination with a labile, non-accumulable precursor of acetyl phosphate as follows: