Respiration and protein synthesis in Escherichia coli membrane-envelope fragments. 3. Electron microscopy and analysis of the cytochromes

Molecular cloning and characterization of cytochrome P450 and ferredoxin genes involved in bisphenol A degradation in Sphingomonas bisphenolicum strain AO1

AIMS

To clone and characterize the genes bisdA and bisdB, encoding Ferredoxin(bisd) (Fd(bisd)) and cytochrome P450(bisd) (P450(bisd)), respectively, from the bisphenol A (BPA) degrading Sphingomonas bisphenolicum strain AO1.

METHODS AND RESULTS

The 3.7 kb region containing bisdA and bisdB was cloned by genome walking and colony hybridization. The deduced N-terminal amino acid sequences of bisdA and bisdB were consistent with those of Fd(bisd) and P450(bisd) proteins characterized in our previous report. Two transposase genes, tnpA1 and tnpA2, were also located upstream and downstream of bisdAB. From amino acid sequence analysis, P450(bisd) has two conserved regions corresponding to the oxygen and heme binding regions of the bacterial cytochrome P450 family. Fd(bisd) was similar to putidaredoxin-type [2Fe-2S] ferredoxins. Escherichia coli BL21 (DE3) cells bearing bisdB- and bisdAB-recombinant pET19b were able to degrade BPA. A spontaneous mutant, strain AO1L, which was unable to degrade BPA, was isolated from the stock culture, and it was confirmed that strain AO1L had no bisdAB region.

CONCLUSIONS

P450(bisd) monooxygenase sytem, encoded by bisdAB, is one system required for BPA hydroxylation in S. bisphenolicum strain AO1.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results indicate that bisdAB are key genes for BPA degradation in S. bisphenolicum strain AO1.

Redox properties of beta-type cytochromes in Escherichia coli and rat liver mitochondria and techniques for their analysis

We describe here apparatus and procedures for conducting potentiometric titrations and for analyzing the collected data in terms of the number of components present, their amounts and their midpoint potentials. Using these procedures we have determined the presence of three forms of cytochrome b1 in Escherichia coli with midpoint potentials at pH 7.1 OF about minus 50, plus 110 and plus 220 mV. We were not able to demonstrate a change in any of these potentials by the addition of phosphate, ATP, or 2, 4-dinitrophenol. We have been able to confirm the presence of two forms of cytochrome b in non-energized mitochondria and the apparent conversion of the low-potential component to a new high potential component upon energization of the mitochondria. However we cite further experimental data that question the actual conversion of one form of cytochrome b to another. An alternative interpretation based on our analysis suggests that the high voltage component may be present in a masked form in the non-energized mitochondria.

Respiration and protein synthesis in Escherichia coli membrane-envelope fragments. VI. Solubilization and characterization of the electron transport chain

Membranes obtained from Escherichia coli have been solubilized with deoxycholate. The solubilized dehydrogenases and cytochromes are not sedimented at 105,000 g. These components readily penetrate the "included space" of Sepharose 4B (Pharmacia Fine Chemicals Inc., Uppsala, Sweden) and polyacrylamide gels and have been fractionated on the basis of molecular size. Solubilization destroys nicotinamide adenine dinucleotide, reduced form (NADH) oxidase and D-lactate oxidase activities, but leaves an appreciable part of the original succinoxidase activity intact. Evidence for a succinate dehydrogenase-cytochrome b(1) complex is given. Menadione added to the solubilized preparation does not elicit NADH oxidase activity nor stimulate the existing succinoxidase activity, but does provoke an active D-lactate oxidase activity. This D-lactate oxidase activity, however, does not use cytochromes and is not sensitive to cyanide.

Respiration and protein synthesis in Escherichia coli membrane-envelope fragments. IV. Chemical and cytological characterization and biosynthetic capabilities of fragments obtained by mild procedures

Membrane-envelope fragments have been isolated from Escherichia coli by comparatively mild techniques. The use of DNAase, RNAase, detergents, sonication, lysozyme, and ethylenediaminetetraacetate were avoided in the belief that rather delicate, but metabolically important, associations may exist between the plasma membrane and various cytoplasmic components. The membrane-envelope fragments have been characterized in terms of their content of major chemical components as well as their electron microscope appearance. Fractions containing membrane-envelope fragments were found to possess appreciable DNA- and protein-synthesizing activities. The fragments were rich in membrane content as determined by reduced nicotinamide adenine dinucleotide (NADH) oxidase activity and deficient in soluble components as measured by NADH dehydrogenase activity. The particulate fraction obtained between 20,000 g and 105,000 g and usually considered a ribosomal fraction was rich in membrane content and had a relatively high capacity for DNA synthesis. Envelope fragments sedimenting at 20,000 g attained very high levels of incorporation of amino acids into protein.

Respiration and protein synthesis in Escherichia coli membrane-envelope fragments. V. On the reduction of nonheme iron and the cytochromes by nicotinamide adenine dinucleotide and succinate

The sensitivity of nicotinamide adenine dinucleotide (NADH) oxidase and succinoxidase to metal chelators, the generation of an electron paramagnetic resonance (EPR) signal upon addition of these substrates, and the rate of formation of the EPR signal relative to the rate of the cytochrome reduction suggest the participation of nonheme iron proteins in the respiratory process of Escherichia coli. The most inhibitory metal chelator, thenoyltrifluoro acetone, inhibited the reduction of nonheme iron and cytochromes but did not prevent the reoxidation of the reduced forms. The EPR signal, dehydrogenase, and oxidase activities evoked by NADH are considerably greater than the corresponding activities evoked by succinate. Because both substrates can reduce almost all of the cytochromes, a model in which fewer succinate dehydrogenase-nonheme iron protein complexes are linked to a common cytochrome chain than NADH dehydrogenase-nonheme iron protein complexes is considered likely.