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At least 181 records · Page 10Linked to original sources
PubMed1972

Restoration of reduced nicotinamide adenine dinucleotide phosphate-nitrate reductase activity of a Neurospora mutant by extracts of various chlorate-resistant mutants of Escherichia coli.

Acid-treated extracts of Escherichia coli were tested for their ability to restore reduced nicotinamide adenine dinucleotide phosphate-nitrate reductase activity to an extract of a Neurospora nit-1 mutant which produces a defective enzyme. With wild-type E. coli this complementation activity was more readily detected in the cytoplasmic fraction, although the nitrate reductase activity was found primarily in the particulate fraction. chlB mutants of E. coli appeared to have more complementation activity in the cytoplasm than was observed in the wild type, but no activity in the particulate fraction. The other chl mutants had little or no activity in either fraction. These results suggest that chlB mutants can produce a component or cofactor which is missing in the other mutants and in the Neurospora mutant, but cannot transfer it to the nitrate reductase enzyme.

Bacterial Proteins↗
PubMed1975

Synthesis of nitrate reductase components in chlorate-resistant mutants of Escherichia coli.

Specific antibody to purified nitrate reductase from Escherichia coli was used to identify enzyme components present in mutants which lack functional nitrate reductase. chlA and B mutants contained all three subunits present in the wild-type enzyme. Different peptides with a broad range of molecular weights could be precipitated from chlCmutants, and chlE mutants contained either slightly degraded enzyme subunits or no precipitable protein. No mutants produced significant amounts of cytoplasmic enzyme. The chlA and B loci are suggested to function in the synthesis and attachment of a molybdenum-containing factor. The chlC locus is suggested to be the structural gene for nitrate reductase subunit A and chlE is suggested to be involved in the synthesis of the cytochrome b1 apoprotein.

Anaerobiosis↗
PubMed1981

Identification of the molybdenum cofactor in chlorate-resistant mutants of Escherichia coli.

Experiments were performed to determine whether defects in molybdenum cofactor metabolism were responsible for the pleiotropic loss of the molybdoenzymes nitrate reductase and formate dehydrogenase in chl mutants of Escherichia coli. In wild-type E. coli, molybdenum cofactor activity was present in both the soluble and membrane-associated fractions when the cells were grown either aerobically or anaerobically, with and without nitrate. Molybdenum cofactor in the soluble fraction decreased when the membrane-bound nitrate reductase and formate dehydrogenase were induced. In the chl mutants, molybdenum cofactor activity was found in the soluble fraction of chlA, chlB, chlC, chlD, chlE, and chlG, but only chlB, chlC, chlD, and chlG expressed cofactor activity in the membrane fraction. The defect in the chlA mutants which prevented incorporation of the soluble cofactor into the membrane also caused the soluble cofactor to be defective in its ability to bind molybdenum. This cofactor was not active in the absence of molybdate, and it required at least threefold more molybdate than did the wild type in the Neurospora crassa nit-1 complementation assay. However, the cofactor from the chlA strain mediated the dimerization of the nit-1 subunits in the presence and absence of molybdate to yield the 7.9S dimer. Growth of chlA mutants in medium with increased molybdate did not repair the defect in the chlA cofactor nor restore the molybdoenzyme activities. Thus, molybdenum cofactor was synthesized in all the chl mutants, but additional processing steps may be missing in chlA and chlE mutants for proper insertion of cofactor in the membrane.

Chlorates↗