Solubilization and Properties of Formate Dehydrogenase and Cytochrome b1 from Escherichia coli*

A preparation containing formate dehydrogenase, cytochrome b1 and nitrate reductas_??_ was solubilized and partially purified from the particulate fraction of E. coli cells growr_??_ anaerobically under the conditions favorable for nitrate respiration. Some properties o_??_ formate dehydrogenase and cytochrome b1 in this purified preparation were investigated It was suggested that formate dehydrogenase is a metalloflavoprotein with essential sulf_??_ hydryl groups. Its activity was strongly bu_??_ reversibly inhibited by molecular oxyge_??_ The prosthetic group of cytochrome b1 was decisively identified as protoheme, and it was found that the cytochrome is autoxidizable. The reduction of cytochrome b1 by formate was shown to require, in addition to formate dehydrogenase, a lipid-soluble factor which could be replaced by vitamin K3 in the solubilized system.We are indefted to Drs. H. Maeno and S. Sakakibara for generous gifts of crude snake venonand crystalline protohemin, respectively.