Archly fiir Mikrobiologie 63, 117--121 (1968) Enzymic Properties of a Mutant of Escherichia coli Lacking Nitrate Reductase W. A. Vr~A~LrS, J. W. T. WIMr~r, and J. A. COLV, Department of Microbiology, University College of South Wales and Monmouthshire, Cardiff, Wales Received May 28, 1968 K12 Summary. A pleiotropic mutant of Escherichia cell KI~ lacking reduced NAD: nitrate oxidoreductase, soluble formate dehydrogenase and membrane-bound formate:ferricytochrome b1 oxidoreduetase is described. Levels of several other enzymes and cytochromes have been measured and found to differ little from those normally present in the wild type with the exceptions of eytoehrome c52~,reduced NAD:cytochrome e oxidoreductase and reduced NAD:nitrite oxidoreductase which are vel T high. Although the affected gene maps in a different position from that reported for chl A by other workers it seems likely that the two loci are identical. Nitrate reductaselcss mutants of Enterobacteriaceae have recently been isolated in two laboratories. The mutations have been found to be pleiotropie causing, in addition to the loss of reduced NAD:nitrate oxidoreductase activity, the loss of chlorate reductase and formate hydrogenlyase in both Aerobacter aerogenes (STOUT~A~E~, 1967) and Escheriehia cell (~:)IEC~AUD et al., 1967). The latter workers have found that at least one of the E. cell mutants which is defective at chl A (PuIG and Azov~L~u 1967; PuIG et al., 1967) lacks a subcellular particle and have suggested that the lost activities are located upon this particle in the wild type (AzovLAr et al., 1967). Recent work in our laboratory has resulted in the isolation of a collection of mutants of E. cell K12 which lack nitrate reductase and map in the same region as one of the mutants described by AzouLAY and co-workers (V~NABLES and Gu~s~, manu- script in preparation). The present communication describes enzymic studies on one of these mutants (collection No. C98). Materials and Methods Bacterial Strains. E. cell K12 AB1621 was used as the wild type and the mutant C98 was derived from this strain. Cell Culture. 11 1 batches of cells were grown anaerobically in complex medium containing glucose (0.40/0, w/v) in a New Brunswick Laboratory fermenter. The cultures were agitated mechanically, gassed with a mixture of N2:C02 (95:5) and kept at pH 6.2 and 37~ throughout growth. Cells were harvested when the optical density (550 m[z) of the culture was between 0.4 and 0.6 and crude ceil-free crushes