Properties of hydrogenase from Azotobacter vinelandii

A comparison of the physical and chemical properties of four cytochromes c from Azotobacter vinelandii

1. A modified method for the separation and purification of four cytochromes c from Azotobacter vinelandii is described. Two new cytochromes c have been purified and are designated cytochromes c(551) and c(555). 2. Additional evidence is presented to establish the dihaem nature of cytochrome c(4). Ultracentrifugation data indicated similar molecular weights for the native and the denatured protein. Cleavage with CNBr yielded seven peptides; the amino acid compositions of the purified peptides were determined. Only one haem peptide was recovered. 3. Cytochromes c(551) and c(555) were characterized as acidic proteins of molecular weights about 12000. The spectral properties, isoelectric points, ;maps' of peptides from CNBr cleavage and amino acid compositions were determined for these two proteins. 4. The spectral properties, isoelectric points, molecular weights, CNBr peptide ;maps', amino acid compositions, relative oxidation-reduction potentials and e.p.r. (electron-paramagnetic-resonance) spectra of the four cytochromes c were compared. Cytochrome c(4) and cytochrome c(551) appear to be distinct proteins. The distinction between cytochromes c(5) and c(555) was not as clear, and our data are inadequate to establish firmly that they are distinct proteins. 5. The dihaem nature of cytochrome c(4) is evident in its e.p.r. spectrum. The e.p.r. spectra are similar to the spectra of mammalian cytochromes c.

Phosphorylation in hydrogen bacteria

The electron-transport system of cell-free extracts obtained from Hydrogenomonas H-20 has been studied with particular reference to phosphorylation associated with the oxyhydrogen reaction. Cell-free preparations of this organism exhibit oxidative phosphorylation with hydrogen and succinate as electron donors. This activity could be uncoupled with a number of agents. Ratios of phosphorylative activity to oxidative activity observed varied from 0.2 to 0.7. Factors affecting the efficiency of phosphorylation were examined. Inhibitor and spectrophotometric studies indicated that phosphorylation with hydrogen as electron donor occurs exclusively at a site in an abbreviated electron transport chain between H(2) and cytochrome b. The possible occurrence of a cytochrome b oxidase and the requirement for a quinone are discussed, as well as the correlation between the abbreviated pathway and the energy generation by the cell. Evidence is presented which indicates that nicotinamide adenine dinucleotide does not participate in the hydrogen oxidation path which is coupled to adenosine triphosphate formation.

SUBMICROSCOPIC PARTICLES IN EXTRACTS OF AZOTOBACTER AGILIS1

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