Characterization of purified nitrate reductase A and chlorate reductase C from Proteus mirabilis.

Nitrate reductase A has been solubilized from purified cytoplasmic membranes by extraction with tert-amyl alcohol. The resulting aqueous solution contained monomeric reductase which polymerized slowly to dimers and tetramers with sedimentation coefficients of respectively 10.5, 16 and 23 Svedbergunits. The polymerization could be stopped to some extent by addition of a small amount of Triton X-100. These distinct entities of nitrate reductase A were separable on electro-focusing, DEAE-column chromatography and polyacrylamide gel electrophoresis, and have been proved to consist of similar subunits with molecular weights of 104000, 63000, and 56000 daltons. The molecular weights of monomeric nitrate reductase A was found to be about 240000 daltons. Chlorate reductase C has been solubilized by a similar procedure, resulting in only monomeric enzyme. Chlorate reductase C exhibited a sedimentation coefficient of 7.7 Svedbergunits, an isoelectric point of pH = 4.55 and a molecular weight of approx. 180000 daltons. It was found to consist of three subunits with molecular weights of 75000, 63000 and 56000 daltons. The latter two subunits are most probably common in nitrate reductase A and chlorate reductase C.