Extracts of Escherichia coli contain an enzyme system which catalyzes an oxidative decarboxylation of pyruvate represented by reaction 1. 1, 2-3 acetyl CoA+ COZ+ DPNH+ H+(1) We have obtained highly purified preparations (250-fold purification) of this system from extracts of the Crookes strain. It is apparently an enzyme~ omplex,~ and sediments in the ultracentrifuge (1 to 2 hr. at 144,000 X g) as a dark yellow, fluorescent pellet. The ...