Nitrogenase of Klebsiella pneumoniae. Interaction of the component proteins studied by ultracentrifugation

Sedimentation-velocity analyses of mixtures of the component proteins of nitrogenase of Klebsiella pneumoniae at a 1:1 molar ratio, showed a single peak of sedimentation coefficient (12.4S) considerably greater than that obtained for the larger (Fe+Mo-containing) protein centrifuged alone (10.4S). When the ratio exceeded 1:1 (the smaller Fe-containing protein in excess) an additional peak corresponding in sedimentation coefficient (about 4.5S) to free Fe-containing protein appeared. When proteins, which had been inactivated by exposure to air were used, no interaction occurred. Na(2)S(2)O(4) at 2mm both reversed and prevented interaction between the two proteins; sedimentation coefficients corresponded to those of the proteins when centrifuged alone. These results demonstrate the formation of a complex between the nitrogenase proteins, and, together with data of activity titration curves, are consistent with the formulation of the nitrogenase complex of K. pneumoniae as (Fe-containing protein)-(Fe+Mo-containing protein).

Studies by electron paramagnetic resonance on the catalytic mechanism of nitrogenase of Klebsiella pneumoniae

The properties and catalytic reactions of the enzyme nitrogenase purified from Klebsiella pneumoniae were studied by electron-paramagnetic-resonance (e.p.r.) spectroscopy at temperatures down to 8 degrees K. The two protein fractions, Kp1 (the iron-molybdenum protein) and Kp2 (the iron protein), were examined alone and in steady-state mixtures and also in pre-steady-state experiments, by using the rapid-freezing method. Kp1 protein in dithionite solution shows a rhombic type of spectrum with g(1) 4.32, g(2) 3.63, g(3) 2.009 at pH6.8 (0 degrees C). Small changes in the spectrum produced by protons (pK=8.7 at 0 degrees C) or by acetylene indicate binding of these oxidizing substrates to this protein fraction. Kp2 protein shows a rhombic spectrum with g(1) 2.053, g(2) 1.942, g(3) 1.865, which integrates to about 0.45 electron/molecule. Binding of ATP, with a dissociation constant of 4x10(-4)m, changes the spectrum to an axial form with g( parallel) 2.036, g( perpendicular) 1.929, thus indicating a conformation change of Kp2 protein. The Kp2 protein spectrum disappears reversibly on cautious oxidation. The signals of both proteins are diminished in their steady-state mixtures, obtained in the presence of ATP and dithionite (with an ATP-generating system and Mg(2+) ions) and with protons, N(2) or acetylene as oxidizing substrate. At the same time as dithionite is consumed in such reactions, the Kp1 protein signal is gradually restored and the Kp2 protein signal diminishes to zero. In rapid-freezing experiments the signals from the two proteins decreased at indistinguishable rates (t((1/2)) about 10ms), then they remained constant. Results are interpreted in terms of a scheme in which reducing equivalents pass from dithionite to Kp2 protein, then, in an ATP-dependent reaction to Kp1 protein, this being finally reoxidized by N(2) or another oxidizing substrate. In this scheme Kp1 protein cycles between its signal-giving state and a very highly reduced signal-free state.

Penicillinases of Klebsiella pneumoniae and their phylogenetic relationship to penicillinases mediated by R factors

On the assumption that the penicillinase determinants on a group of R factors conferring ampicillin resistance have a phylogenetically close relationship to the penicillinase gene of the Klebsiella group, the penicillinases from four strains of K. pneumoniae, GN69, GN1103R(-), GN422, and GN118, were purified 230- to 1,000-fold and compared with the known two R-factor-mediated penicillinases. By gel filtration on Sephadex G-75, the molecular weights were estimated to be 17,400, 18,100, 20,000 and 18,300, respectively, which are slightly lower than those of the R-factor penicillinases. The isoelectric points of the Klebsiella penicillinases were not in agreement with those of the R-factor penicillinases. All the enzymes showed a pH optimum between 6.3 to 7.2 and a temperature optimum of 45 C, and those properties, together with behavior towards inhibitors, were about the same as those in the R-factor penicillinases. The substrate specificity and the Michaelis constants of the Klebsiella penicillinases for penicillins and cephaloridine were broadly similar to those of the R-factor penicillinases, however, some variations were found even among the four penicillinases of K. pneumoniae. The reactivities of the four penicillinases of K. pneumoniae with the antiserum against one R-factor penicillinase were tested, and three of the four Klebsiella penicillinases were found to be indistinguishable immunologically from both R-factor penicillinases. The remaining Klebsiella penicillinase, from GN1103R(-), showed an immunological partial homology with the R-factor penicillinases.

Aminoglycoside antibiotic-inactivating enzymes in actinomycetes similar to those present in clinical isolates of antibiotic-resistant bacteria

Various species of Streptomyces possess aminoglycoside-modifying enzymes. Streptomyces kanamyceticus contains an enzyme that acetylates the 6'-amino group of kanamycin A and B, gentamicin C(1a), and neomycin. Streptomyces spectabilis produces an enzyme that acetylates the 2'-amino group of the hexose ring of gentamicin C(1a). These enzymes catalyze reactions identical to those catalyzed by enzymes found in gram-negative bacteria containing R(antibiotic resistance)-factors. The discovery of these enzymes suggests the possibility of an evolutionary relationship between the aminoglycosideinactivating enzymes (produced by resistance determinants) in bacteria containing R-factors and similar enzymes found in the actinomycetes.

Nitrogenase of Klebsiella pneumoniae: evidence for an adenosine triphosphate-induced association of the iron-sulphur protein

The effect of various nucleotides on the Fe-containing component of nitrogenase of Klebsiella pneumoniae was investigated by ultracentrifugation and thiol-group reactivity towards 5,5'-dithiobis-(2-nitrobenzoate). In the absence of Na(2)S(2)O(4), ATP and ADP produced changes in sedimentation behaviour and thiol-group reactivity consistent with association of the protein.

Nitrogen fixation by Klebsiella grown in the presence of oxygen

Several facultative asymbiotic N2-fixing bacteria exhibited nitrogenase activity when grown in the presence of air and a limiting amount of fixed nitrogen. One isolate (S-4) identified as Klebsiella was examined in more detail for oxygen effects. Nitrogenase was not detectable in highly aerated submerged cultures but was detectable in shaken and continuous cultures at dissolved oxygen tensions of 3 and 10 mm of Hg respectively. No nitrogenase activity was found in cells from continuous cultures maintained at a dissolved oxygen tension of 15 mm of Hg or above. The nitrogenase activity in whole cells was not oxygen dependent but was oxygen tolerant.

Nitrogenase of Klebsiella pneumoniae. Purification and properties of the component proteins

1. Nitrogenase from the facultative anaerobe Klebsiella pneumoniae was resolved into two protein components resembling those obtained from other nitrogen-fixing bacteria. 2. Both proteins were purified to homogeneity as shown by the criteria of disc electrophoresis and ultracentrifugal analysis. 3. The larger component had a mol.wt. of 218000 and contained one Mo atom, 17Fe atoms and 17 acid-labile sulphide groups/mol; it contained two types of subunit, present in equal amounts, of mol.wts. 50000 and 60000. All the common amino acids were present, with a predominance of acidic residues. The apparent partial specific volume was 0.73; ultracentrifugal analysis gave s(0) (20,w)=11.0S and D(0) (20,w)=4.94x10(-7)cm(2)/s. The specific activities (nmol of product formed/min per mg of protein) when assayed with the second nitrogenase component were 1500 for H(2) evolution, 380 for N(2) reduction, 1200 for acetylene reduction and 5400 for ATP hydrolysis. The reduced protein showed electron-paramagnetic-resonance signals at g=4.3, 3.7 and 2.015; the Mössbauer spectrum of the reduced protein consisted of at least three doublets. The u.v. spectra of the oxidized and reduced proteins were identical. On oxidation the absorbance increased generally throughout the visible region and a shoulder at 430nm appeared. The circular-dichroism spectra of both the oxidized and reduced proteins were the same, consisting mainly of a negative trough at 220nm. 4. The smaller component had mol.wt. 66800 and contained four Fe atoms and four acid-labile sulphide groups in a molecule comprising two subunits each of mol.wt. 34600. All common amino acids except tryptophan were present, with a predominance of acidic residues. The apparent partial specific volume calculated from the amino acid analysis was 0.732, which was significantly higher than that obtained from density measurements (0.69); ultracentrifugal analysis gave s(0) (20,w)=4.8S and D(0) (20,w)=5.55x10(-7)cm(2)/s. The specific activities (nmol of product formed/min per mg of protein) were 1050 for H(2) evolution, 275 for N(2) reduction, 980 for acetylene reduction and 4350 for ATP hydrolysis. The protein was not cold-labile. The reduced protein showed electron-paramagnetic-resonance signals in the g=1.94 region. The Mössbauer spectrum of the reduced protein consisted of a doublet at 77 degrees K. The u.v. spectra of reduced and O(2)-inactivated proteins were identical, and inactivation by O(2) generally increased the absorbance in the visible region and resulted in a shoulder at 460nm. The circular-dichroism spectra exhibited a negative trough at 220nm and inactivation by O(2) decreased the depth of the trough. 5. The reduction of N(2) and acetylene, and H(2) evolution, were maximal at a 1:1 molar ratio of the Fe-containing protein to the Mo-Fe-containing protein; excess of the Mo-Fe-containing protein was inhibitory. All reductions were accompanied by H(2) evolution. The combined proteins had no ATP-independent hydrogenase activity.

Comparison of the substrate specificities of the -lactamases from Klebsiella aerogenes 1082E and Enterobacter cloacae P99

A potent beta-lactamase (EC 3.5.2.6) produced by a strain of Klebsiella aerogenes (K. pneumoniae), 1082E, isolated from a hospital patient, has been examined. Its properties were different from those of most gram-negative beta-lactamases previously reported. The enzyme has been partly purified, and its activity against a range of substrates has been compared with that of the enzyme from Enterobacter cloacae (Aerobacter cloacae) P99. The K. aerogenes enzyme, although predominantly a penicillinase, had a wide range of specificity. In addition to hydrolyzing the cephalosporins, it attacked the normally beta-lactamaseresistant compounds methicillin and cloxacillin as well as cephalosporin analogues with the same acyl substituents. The results obtained with the E. cloacae enzyme confirmed its cephalosporinase activity and showed that, unlike the enzyme from K. aerogenes, it was relatively inactive against the penicillins.