Open AccessSelenium increases hydrogenase expression in autotrophically cultured Bradyrhizobium japonicum and is a constituent of the purified enzyme
Author(s) -
P Boursier,
F. J. Hanus,
H. Papen,
Mary Misko Becker,
Sterling A. Russell,
Harold J. Evans
Publication year - 1988
Publication title -
journal of bacteriology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.652
H-Index - 246
eISSN - 1067-8832
pISSN - 0021-9193
DOI - 10.1128/jb.170.12.5594-5600.1988
Subject(s) - bradyrhizobium japonicum , derepression , hydrogenase , selenium , enzyme , biology , biochemistry , azotobacteraceae , bacteria , chemistry , rhizobiaceae , nitrogenase , gene expression , gene , nitrogen fixation , psychological repression , genetics , organic chemistry , symbiosis
We have investigated the effect of added selenite on autotrophic growth and the time course of hydrogen oxidation derepression in Bradyrhizobium japonicum 122DES cultured in a medium purified to remove selenium compounds. In addition, hydrogenase was purified to near homogeneity and examined for the specific incorporation of Se into the enzyme. The addition of Se at 0.1 microM significantly increased total cell protein and hydrogenase specific activity of harvested cells. Also, the addition of SeO3(2-) enhanced the time course of hydrogenase derepression by 133%, whereas VO3, AsO2(2-), SO2(2-), and TeO3(2-) failed to substantially affect hydrogenase derepression. During the final chromatographic purification of hydrogenase, a striking coincidence in peaks of protein content, Se radioactivity, and hydrogenase activity of fractions was obtained. The total Se content expressed per milligram of protein increased manyfold during the purification procedure. The mean Se content of the purified hydrogenase was 0.56 +/- 0.13 mol of Se per mol of enzyme. These results indicate that Se is an important element in the H2 metabolism of B. japonicum and that hydrogenase from B. japonicum is a seleno protein.