Multiple forms of bacterial hydrogenases

Solubilization and properties of a particulate hydrogenase from Methanobacterium strain G2R

Mechanical disruption of cells of Methanobacterium strain G2R resulted in a 78-fold increase in the specific activity of the hydrogenase as measured by the benzyl viologen reduction assay. Approximately 50% of the activity in disrupted cells was associated with the particulate fraction. Between 69 and 85% of the particulate hydrogenase was released by treatment with the detergents Triton X-100, deoxycholate, and octyl-beta-d-glucopyranoside. The relative electrophoretic mobilities of the soluble hydrogenases were identical, indicating that G2R possessed a single electrophoretically distinct hydrogenase. The particulate enzyme was inactivated by oxygen and could be reactivated with dithionite or glucose plus glucose oxidase. The enzyme had a pH optimum of 8.5 and resisted heating at 52 but not 77 degrees C. A number of nonspecific dyes, flavin adenine dinucleotide, and riboflavin 5'-phosphate were effective electron acceptors; oxidized nicotinamide adenine dinucleotide, nicotinamide adenine dinucleotide phosphate, and factor 420 were apparently not reduced. Hydrogenase activity was inhibited by p-hydroxymercuribenzoate, cyanide, chloroform, and chloramphenicol. The molecular weight of the solubilized enzyme was 900,000, with subunits of molecular weights 38,500, 50,700, and approximately 80,000. It is suggested that, in intact cells of G2R, the large hydrogenase complex is loosely bound to the cell wall or membrane.

Localization and stability of hydrogenases from aerobic hydrogen bacteria

Alcaligenes eutrophus strains H 16, B 19, G 27 and N9A contained two different hydrogenases. One enzyme catalyzed the reduction of NAD by hydrogen and was strictly localized in the soluble cell fraction. While the second enzyme was found to be particulate and unable to react with NAD. All other tested strains, Alcaligenes paradoxus SA 29, Pseudomonas facilis, P. palleronii RH 2, Pseudomonas sp. strain GA 3, Paracoccus denitrificans, Aquaspirillum autotrophicum SA 32, and Corynebacterium autotrophicum 14g and 7C contained only a single enzyme exclusively bound to membranes. This was established using fractional centrifugation, indicator enzyme systems, gently methods of cell disintegration and discontinuous sucrose density gradient centrifugation. In cell-free extracts obtained by rough disruption (sonication) of cells, hydrogenase was associated to particles of different size and sedimentation velocity. A partial solubilization of hydrogenase caused by sonication was observed with P. facilis. Without exception, the particulate hydrogenases were found (1) to be unable to reduce pyridine nucleotides, and (2) to reduce methylene blue at an extremely high activity. The eminent reaction rate of 34 micronmoles H2 oxidized per min and mg protein has been determined in particle suspensions of Pseudomonas sp. strain GA 3. All hydrogenases were stable during storage under hydrogen atmosphere, except the soluble enzyme for A. eutrophus H 16 which was shown to be more stable under aerobic conditions.

Purification and properties of soluble hydrogenase from Alcaligenes eutrophus H 16

The soluble hydrogenase (hydrogen: NAD+ oxidoreductase, EC 1.12.1.2) from Alcaligenes eutrophus H 16 was purified 68-fold with a yield of 20% and a final specific activity (NAD reduction) of about 54 mumol H2 oxidized/min per mg protein. The enzyme was shown to be homogenous by polyacrylamide gel electrophoresis. Its molecular weight and isoelectric point were determined to be 205 000 and 4.85 respectively. The oxidized hydrogenase, as purified under aerobic conditions, was of high stability but not reactive. Reductive activation of the enzyme by H2, in the presence of catalytic amounts of NADH, or by reducing agents caused the hydrogenase to become unstable. The purified enzyme, in its active state, was able to reduce NAD, FMN, FAD, menaquinone, ubiquinone, cytochrome c, methylene blue, methyl viologen, benzyl viologen, phenazine methosulfate, janus green, 2,6-dichlorophenoloindophenol, ferricyanide and even oxygen. In addition to hydrogenase activitiy, the enzyme exhibited also diaphorase and NAD(P)H oxidase activity. The reversibility of hydrogenase function (i.e. H2 evolution from NADH, methyl viologen and benzyl viologen) was demonstrated. With respect to H2 as substrate, hydrogenase showed negative cooperativity; the Hill coefficient was n = 0.4. The apparent Km value for H2 was found to be 0.037 mM. The absorption spectrum of hydrogenase was typical for non-heme iron proteins, showing maxima (shoulders) at 380 and 420 nm. A flavin component could be extracted from native hydrogenase characterized by its absorption bands at 375 and 447 nm and a strong fluorescense at 526 nm.

Evidence for the periplasmic location of hydrogenase in Desulfovibrio gigas

Hydrogenase has been found to be located in the periplasmic space of Desulfovibrio gigas, and it is proposed that hydrogenase plays an important and specific role in interspecies hydrogen transfer.

Purification and properties of a hydrogenase from Desulfovibrio vulgaris

The soluble hydrogenase of Desulfovibrio vulgaris was purified and some of its properties are described. The molecular weight was determined for the enzyme by sedimentation equilibrium (45,400) and amino acid analysis (44,800). The hydrogenase appears to be a loosely coiled molecule or to have a high axial ratio, which is reflected in an unusually low sedimentation coefficient (2.58S) and a low diffusion coefficient (D 5.85). The molecular weight of the hydrogenase (41,000), as calculated by the Svedberg equation, was in general agreement with the sedimentation equilibrium molecular weight. Amino acid analysis revealed the presence of six halfcystine residues per mole of enzyme and a total of 417 amino acid residues. The specificity of the hydrogenase and its capacity to reduce certain low potential dyes and cytochrome c(3) was studied. Metal analysis of the hydrogenase indicated the presence of 1 mole of ferrous iron per mole of enzyme.

Hydrogen metabolism by Rhodomicrobium vannielii

Under appropriate cultural conditions, cell suspensions of Rhodomicrobium vannielii effect two distinct photoreactions involving molecular hydrogen: (i) the photoreduction of carbon dioxide, and (ii) the photoproduction of hydrogen.

Zone electrophoresis of enzymes in bacterial taxonomy

The electrophoretic mobilities in starch gels have been determined for eight enzymes in extracts of representative cultures of members of the family Enterobacteriaceae. These values were compared with each other and with those obtained from certain bacteria not in this family. The migrations of the eight enzymes were virtually identical for each of eight strains of Escherichia coli and for two species of Shigella. A number of these enzymes appeared to be identical in other organisms believed to be closely related to E. coli (Salmonella), and the number of differences increased in organisms which appeared to have lesser degrees of relatedness by other criteria (deoxyribonucleic acid base compositions, overall similarity).

Isolation and role of nonheme iron protein in Clostridium botulinum

A type of iron-bound protein was isolated from Clostridium botulinum by a modification of the method used for isolating ferredoxin from C. pasteurianum. This method involved acetone and diethylaminoethyl cellulose treatments followed by ammonium sulfate fractionation. The protein exhibited maximal absorption in the ultraviolet region near 260 mmu. Portions of the isolated iron protein were separated by disc electrophoresis and, following specific iron-bound protein staining, showed a positive reaction in the same position on the gel column as was first demonstrated by use of cell-free extract. Evidence accumulated by use of a cell-free extract of C. botulinum suggests that pyruvate is metabolized through a phosphoroclastic system as demonstrated in other clostridia. It is probable that ferredoxin is an electron mediator between pyruvic oxidase and hydrogenase for hydrogen evolution and acetyl phosphate formation.

Comparative control of a branch-point enzyme in microorganisms

Thirty-two genera of microorganisms were identified with one of six distinctive control patterns for the enzyme 3-deoxy-d-arabino-heptulosonate-7-phosphate synthetase. These patterns included sequential feedback inhibition, isoenzyme feedback inhibition, cumulative feedback inhibition, and three (apparent) simple one-effector patterns. Documentation is provided of an overwhelming tendency for control patterns to be strongly conserved among the member species of the various genera that were examined.