D-Fructose dehydrogenase was solubilized and purified from the membrane fraction of glycerol-grown Gluconobacter industrius IFO 3260 by a procedure involving solubilization of the enzyme with Triton X-100 and subsequent fractionation on diethylaminoethyl-cellulose and hydroxylapatite columns. The purified enzyme was tightly bound to a c-type cytochrome and another peptide existing as a dehydrogenase-cytochrome complex. The purified enzyme was deemed pure by analytical ultracentrifugation as well as by gel filtration on a Sephadex G-200 column. The molecular weight of the enzyme complex was determined to be about 140,000, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed the presence of three components having molecular weights of 67,000 (dehydrogenase), 50,800 (cytochrome c), and 19,700 (unknown function). Only D-fructose was readily oxidized by the enzyme in the presence of dyes such as ferricyanide, 2,6-dichlorophenolindophenol, or phenazine methosulfate. Nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate, and oxygen did not function as electron acceptors. The optimum pH of D-fructose oxidation was 4.0. The enzyme was stable at pH 4.5 to 6.0 Stability of the purified enzyme was much enhanced by the presence of detergent in the enzyme solution. Removal of detergent from the enzyme solution facilitated the aggregation of the enzyme and caused its inactivation. An apparent Michaelis constant for D-fructose was observed to be 10(-2) M with the purified enzyme. D-Fructose dehydrogenase was shown to be a satisfactory reagent for microdetermination of D-fructose.
A bacterial strain that can utilize several kinds of alcohols as its sole carbon and energy sources was isolated from soil and tentatively identified as Pseudomonas putida HK5. Three distinct dye-linked alcohol dehydrogenases (ADHs), each of which contained the prosthetic group pyrroloquinoline quinone (PQQ), were formed in the soluble fractions of this strain grown on different alcohols. ADH I was formed most abundantly in the cells grown on ethanol and was similar to the quinoprotein ADH reported for P. putida (H. Görisch and M. Rupp, Antonie Leeuwenhoek 56:35-45, 1989) except for its isoelectric point. The other two ADHs, ADH IIB and ADH IIG, were formed separately in the cells grown on 1-butanol and 1,2-propanediol, respectively. Both of these enzymes contained heme c in addition to PQQ and functioned as quinohemoprotein dehydrogenases. Potassium ferricyanide was an available electron acceptor for ADHs IIB and IIG but not for ADH I. The molecular weights were estimated to be 69,000 for ADH IIB and 72,000 for ADH IIG, and both enzymes were shown to be monomers. Antibodies raised against each of the purified ADHs could distinguish the ADHs from one another. Immunoblot analysis showed that ADH I was detected in cells grown on each alcohol tested, but ethanol was the most effective inducer. ADH IIB was formed in the cells grown on alcohols of medium chain length and also on 1,3-butanediol. Induction of ADH IIG was restricted to 1,2-propanediol or glycerol, of which the former alcohol was more effective. These results from immunoblot analysis correlated well with the substrate specificities of the respective enzymes. Thus, three distinct quinoprotein ADHs were shown to be synthesized by a single bacterium under different growth conditions.
Quinohemoprotein amine dehydrogenase (AMDH) was purified and crystallized from the soluble fraction of Pseudomonas putida IFO 15366 grown on n-butylamine medium. AMDH gave a single component in analytical ultracentrifugation showing an intrinsic sedimentation coefficient of 5.8s. AMDH showed a typical absorption spectrum of cytochrome c showing maxima at 554, 522, 420, and 320 nm in the reduced form and one peak at 410 nm, a shoulder at 350 nm, and a broad hill around 530 nm in the oxidized form. The oxidized enzyme was specifically reduced by the addition of amine substrate. AMDH was composed of three different subunits, 60, 40, and 20 kDa, with the total molecular weight of 120,000. Two moles of heme c were detected per mole of AMDH and the 60-kDa subunit was found to be the heme c-carrying subunit. By redox-cycling quinone staining, a positive reaction band corresponding to the 20-kDa subunit was detected after developed by SDS-PAGE, but the 20 kDa band was scarcely stained by conventional protein staining. Only a silver staining method was possible to detect the subunit after the protein was developed by SDS-PAGE. p-Nitrophenylhydrazine-inhibited AMDH was dissociated into subunits and the 20-kDa subunit showed an absorption maximum at 455 nm, indicating Schiff base formation between the carbonyl cofactor in AMDH and the carbonyl reagent. Thus, AMDH is different from nonheme quinoprotein methylamine dehydrogenase and aromatic amine dehydrogenase in many respects. The presence of an azurin-like blue protein was identified and purified from the same cell-free extract of P. putida as AMDH was purified. The blue protein was reduced specifically during AMDH reaction, suggesting that the blue protein is the direct electron acceptor in amine oxidation. The amine oxidation system was reconstituted successfully only by AMDH, the blue protein, and the cytoplasmic membranes of the organism. The function of the 40-kDa subunit is unknown at the moment. The properties of AMDH were compared with other bacterial amine dehydrogenases so far reported.
There was found to be a KCN-insensitive, alternate oxidase chain branching from the ordinary oxidase chain in the respiratory chain of Pseudomonas aeruginosa grown aerobically. The alternate oxidase activity was highly resistant to KCN, and had a lower affinity for oxygen than ordinary cytochrome oxidase did. The branching point of the alternate oxidase chain from the ordinary oxidase chain was shown to be localized behind cytochrome b. The KCN-insensitive alternate oxidase chain was inhibited slightly with antimycin A and intensively with 2-thenoyltrifluoroacetone. The former inhibited the respiration behind cytochrome b and the latter before cytochrome b. N,N,N',N'-Tetramethyl-p-phenylenediamine oxidase-negative mutant (T105) was prepared from P. aeruginosa. The mutant clearly lacked a functional ordinary cytochrome oxidase, but had the KCN-insensitive alternate oxidase chain and could grow aerobically. The KCN-insensitive alternate oxidase chain had a H+/O ratio of 4, suggesting the existence of two energy-coupling sites in the chain. Under the conditions where both ordinary oxidase and alternate oxidase chains were functioning, the H+/O ratio of the parent strain was 5.6. From these data, we also discuss the energetics of the ordinary oxidase chain in the respiratory chain of aerobic P. aeruginosa.
Acinetobacter calcoaceticus is known to contain soluble and membrane-bound quinoprotein D-glucose dehydrogenases, while other oxidative bacteria contain the membrane-bound enzyme exclusively. The two forms of glucose dehydrogenase were believed to be the same enzyme or interconvertible forms. Previously, Matsushita et al. [(1988) FEMS Microbiol. Lett 55, 53-58] showed that the two enzymes are different with respect to enzymatic and immunological properties, as well as molecular weight. In the present study, we purified both enzymes and compared their kinetics, reactivity with ubiquinone homologues, and immunological properties in detail. The purified membrane-bound enzyme had a molecular weight of 83,000, while the soluble form was 55,000. The purified enzymes exhibited totally different enzymatic properties, particularly with respect to reactivity toward ubiquinone homologues. The soluble enzyme reacted with short-chain homologues only, whereas the membrane-bound enzyme reacted with long-chain homologues including ubiquinone 9, the native ubiquinone of the A. calcoaceticus. Furthermore, the two enzymes were distinguished immunochemically; the membrane-bound enzyme did not cross-react with antibody raised against the soluble enzyme, nor did the soluble enzyme cross-react with antibody against the membrane-bound enzyme. Thus, each glucose dehydrogenase is a molecularly distinct entity, and the membrane-bound enzyme only is coupled to the respiratory chain via ubiquinone.
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