Cytochrome Oxidase Activity In Cells Research Articles

The Bradyrhizobium japonicum fixGHIS genes are required for the formation of the high-affinity cbb3-type cytochrome oxidase.

We report structural and functional analyses of the Bradyrhizobium japonicum fixGHIS genes, which map immediately downstream of the fixNOQP operon for the symbiotically essential cbb3-type heme-copper oxidase complex. Expression of fixGHIS, like that of fixNOQP, is strongly induced in cells grown microaerobically or anaerobically. A fixGHI deletion led to the same prominent phenotypes as those known from a fixNOQP deletion: defective symbiotic nitrogen fixation (Fix-) and decreased cytochrome oxidase activity in cells grown under oxygen deprivation. Only traces, if any, of cytochrome cbb3 subunits were present in membranes isolated from the delta fixGHI strain, as revealed by Western blot analysis with subunit-specific antibodies. This effect was not due to lack of fixNOQP transcription. The results suggested a critical involvement of the fixGHIS gene products in the assembly and/or stability of the cbb3-type heme-copper oxidase. On the basis of sequence similarities between the FixI protein and a Cu-transporting P-type ATPase (CopA) of Enterococcus hirae, and between FixG and a membrane-bound oxidoreductase (RdxA) of Rhodobacter sphaeroides, we postulate that a membrane-bound FixGHIS complex might play a role in uptake and metabolism of copper required for the cbb3-type heme-copper oxidase.

Induction of cytochromes in human cells by oxygen.

The mechanism of cytochrome induction in human cells was investigated. Cultured fibroblasts grown in low oxygen had markedly reduced contents of cytochromes A + A(3), B, and C + C(1) as measured by absorption spectra. Chloramphenicol but not cycloheximide or actinomycin blocked the initial increase in cytochrome oxidase activity in cells shifted from low to ambient oxygen, suggesting that initiation of enzyme induction requires mitochondrial but not cytoplasmic protein synthesis or transcription of nuclear genes. Turnover of cytochrome oxidase was demonstrated in cells in stationary phase.

Demonstration by the Nadi Reaction of Cytochrome Oxidase Activity in Cells of the Lymphoid and Myeloid Series Obtained from Normal Individuals and Patients Suffering from Hodgkin’s and Other Diseases

Abstract Using the Nadi reaction, cytochemical studies of the cytochrome oxidase activity of cells of lymphoid and myeloid tissue were carried out. Normal cells and those from patients with Hodgkin’s disease and leukemia were examined. With the exception of monocytes and macrophages cells from lymph nodes, spleen, bone marrow and peripheral blood show a low level of cytochrome activity when compared with myocardial, liver and renal tubular epithelium. Leukemic cells and those from lymph nodes affected by Hodgkin’s disease contain about the same degree of cytochrome activity as their normal counterparts, under the conditions of this study. The cytoplasmic particles stained by the Nadi reaction correspond in size, distribution and number to particles which can be stained supravitally by janus green.