Effects of tungstate and molybdate on the in vitro reconstitution of nitrate reductase inEscherichia coliK-12

The inducible trimethylamine-N-oxide reductase of Escherichia coli K12: biochemical and immunological studies

The inducible trimethylamine-N-oxide reductase which migrates on non-denaturing polyacrylamide gels with an RF of 0.22, has been purified from the soluble fraction of wild-type E. coli K12. The molecular weight of the purified enzyme estimated by molecular-sieve chromatography is about 230,000. It is composed of two subunits of molecular weight 110,000. Antiserum specific for the enzyme has been produced. Gel filtration on Sephadex G-200 of the soluble fraction gave two peaks of trimethylamine-N-oxide reductase, one with an Mr of 230,000 and an RF of 0.22, and another with an Mr of 120,000 and an RF of 0.36. Since the anti-trimethylamine-N-oxide reductase serum recognises the two forms and shows a single subunit with an Mr of 110,000, we conclude that in E. coli there is a single inducible trimethylamine-N-oxide reductase which can exist as a dimer or a monomer. Other immunological studies with anti-trimethylamine-N-oxide reductase serum on crude extracts prepared from cells grown in the absence of inducer showed that the constitutive trimethylamine-N-oxide reductase was not recognised by the antiserum. The same analyses carried out on a tor mutant (defective in the structural gene of the inducible enzyme) confirmed without ambiguity that the constitutive enzyme is immunologically distinct from the inducible enzyme. In the same way, using the anti-trimethylamine-N-oxide reductase serum, rocket immunoelectrophoresis analyses were able to show that the inducible apoenzyme is not regulated by the fnr gene product and that molybdate does not seem necessary for the synthesis or stabilisation of this enzyme.

Activation in vitro of respiratory nitrate reductase of Escherichia coli K12 grown in the presence of tungstate. Involvement of molybdenum cofactor

The chlorate-resistant (chlR) mutants are pleiotropically defective in molybdoenzyme activity. The inactive derivative of the molybdoenzyme, respiratory nitrate reductase, present in the cell-free extract of a chlB mutant, can be activated by the addition of protein FA, the probable active product of the chlB locus. Protein FA addition, however, cannot bring about the activation if 10 mM sodium tungstate is included in the culture medium for the chlB strain. The inclusion of a heat-treated preparation of a wild-type or chlB strain prepared after growth in the absence of tungstate, restores the protein-FA-dependent activation of nitrate reductase. All attempts to activate nitrate reductase in extracts prepared from tungstate-grown wild-type Escherichia coli strains failed. It appears that during growth with tungstate, the possession of the active chlB gene product leads to the synthesis of a nitrate reductase derivative which is distinct from that present in the tungstate-grown chlB mutant. Heat-treated preparations from chlA and chlE mutants which do not possess molybdenum cofactor activity fail to restore the activation. Fractionation by gel filtration of the heat-treated preparation from a wild-type strain produced two active peaks in the eluate of approximate Mr 12000 and less than or equal to 1500. The active material in the heat-treated extract was resistant to exposure to proteinases, but after such treatment the active component, previously of approximate Mr 12000, eluted from the gel filtration column with the material of Mr less than or equal to 1500. The active material is therefore of low molecular mass and can exist either in a protein-bound form or in an apparently free state. Molybdenum cofactor activity, assayed by the complementation of the apoprotein of NADPH:nitrate oxidoreductase in an extract of the nit-1 mutant of Neurospora crassa, gave a profile following gel filtration similar to that of the ability to restore respiratory nitrate reductase activity to the tungstate-grown chlB mutant soluble fraction. This was the case even after proteinase treatment of the heat-stable fraction. Analysis of the chlC (narC) mutant, defective in the structural gene for nitrate reductase, revealed that heat treatment is not necessary for the expression of the active component. Furthermore both the active component and molybdenum cofactor activity are present in corresponding bound and free fractions in the non-heat-treated soluble subcellular fraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Cloning of nitrate reductase genes from the cyanobacterium Anacystis nidulans

Anacystis nidulans, a non-nitrogen-fixing cyanobacterium, can fulfill its nitrogen requirement by the assimilation of nitrate. The first step in the pathway, the reduction of nitrate to nitrite, is catalyzed by the molybdo-protein nitrate reductase. In this study, newly developed techniques for gene cloning in A. nidulans R2 were used for the isolation of two genes involved in nitrate reduction. One gene was cloned by complementation of the corresponding mutant; the other gene was picked up from a cosmid gene library by using a restriction fragment containing the transposon-inactivated gene as a probe. Both genes were unlinked single-copy chromosomal genes. Transformation studies provided evidence for the existence of a third locus involved in nitrate reduction.

Identification and purification of a protein involved in the activation of nitrate reductase in the soluble fraction of a chlA mutant of Escherichia coli K12

The isolation and purification of a protein which is the presumed product of the chlA gene has been achieved. This protein, which we have named Protein PA, has been isolated from the soluble fraction of a chlB mutant. The protein was identified by its ability to activate nitrate reductase (EC.1.7.99.4) when mixed with a soluble fraction derived from a chlA mutant. The protein has a molecular weight of about 72 000 and is composed of a single polypeptide chain. Antiserum specific for Protein PA has been produced. Removal of Protein PA from the soluble fraction of chlB mutant by immunoprecipitation with this antiserum leads to the loss of the ability of the preparation to activate nitrate reductase when mixed with a soluble fraction from a chlA mutant. Protein PA, therefore, performs an essential but as yet undefined role in the activation process. Employing this antiserum Protein PA could be quantified by rocket immunoelectrophoretic analysis. The activity of the isolated Protein PA is low, since comparatively large amounts of Protein PA are required to activate the nitrate reductase present in the soluble fraction of the chlA mutant. The mixing of Protein PA with the chlA mutant soluble fraction leads to activation of nitrate reductase in both a soluble and a membranous form, as is the case when the complete soluble fraction of the chlB mutant is used in place of Protein PA. After activation, however, only a small proportion (15%) of the Protein PA is associated with the newly formed membranous material.