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PubMed1986

Measurement of proton pump activity of the thermophilic bacterium PS3 and Nitrobacter agilis at the cytochrome oxidase level using total membrane and heptyl thioglucoside.

It is possible to prepare liposomal vesicles by solubilization of total bacterial membranes with n-heptyl beta-D-thioglucoside followed by reconstitution into proteoliposomes by a freeze-thaw-sonication procedure with soybean phospholipids. The resulting proteoliposomes from total membrane fraction of sufficiently aerated cells of the thermophilic bacterium PS3 containing cytochrome aa3 showed a reasonable H+ pumping activity upon addition of reduced cytochrome c. On the other hand, the proteoliposomes reconstituted from air-limited PS3 cells containing cytochrome o and those from Nitrobacter agilis cells containing cytochrome aa3 did not show H+ pumping upon addition of reduced cytochrome c, although the vesicles showed "respiratory control"; 3-4-fold stimulation of oxygen consumption took place upon addition of an uncoupler. In proteoliposomes prepared from PS3 membranes by this method, H+-translocating ATPase (F0 X F1) was successfully reconstituted as well, suggesting that this method has wide applicability for investigation of enzymes catalyzing transmembrane processes.

Bacteria, Aerobic↗
PubMed1994

Pseudomonas aeruginosa nitrite reductase (or cytochrome oxidase): an overview.

The biochemistry and molecular biology of nitrite reductase, a key enzyme in the dissimilatory denitrification pathway of Ps aeruginosa which reduces nitrite to NO, is reviewed in this paper. The enzyme is a non-covalent homodimer, each subunit containing one heme c and one heme d1. The reaction mechanisms of nitrite and oxygen reduction are discussed in detail, as well as the interaction of the enzyme with its macromolecular substrates, azurin and cytochrome c551. Special attention is paid to new structural information, such as the chemistry of the d1 prosthetic group and the primary sequence of the gene and the protein. Finally, results on the expression both in Ps aeruginosa and in heterologous systems are presented.

Amino Acid Sequence↗
PubMed1991

Reaction of hydrogen peroxide with the rapid form of resting cytochrome oxidase.

The hydrogen peroxide binding reaction has been examined with alkaline-purified resting enzyme in order to avoid mixtures of low pH induced fast and slow conformers. At pH 8.8-9.0 (20 degrees C), the reactivity of resting enzyme was similar to the peroxide-free, pulsed conformer that has been characterized by other investigators. The reaction showed single-phase reactivity at 435 and 655 nm and required a minimum 8:1 molar excess of peroxide (over cytochrome a3) for quantitative reaction. At 16:1, the Soret band was stable for 1.0-1.5 h, but above 80:1, the band began showing generalized attenuation within 1-2 min. The peroxide binding reaction was also associated with an increase in absorbance at 606 nm which correlated with the rate of change at 435 and 655 nm. The observed rate constants at each of these wavelengths showed similar linear dependence on peroxide concentration, giving an average bimolecular rate constant of 391 M-1.s-1 and a Kd of 5.1 microM. The rise phase at 606 nm was observed to saturate at an 8:1 molar excess of peroxide but showed a slow, concentration-dependent first-order decay that gave a bimolecular rate constant and Kd of 38 M-1.s-1 and 20 microM, respectively. The decay was not associated with a change in the Soret absorption or charge-transfer regions, suggesting a type of spectral decoupling. An isosbestic point at 588 nm was consistent with the 606- to 580-nm conversion proposed by other investigators, although direct observation of a new band at 580 nm was difficult.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding Sites↗
PubMed2004

Synergistic anti-tumor effect of ultrasound and hematoporphyrin on sarcoma180 cells with special reference to the changes of morphology and cytochrome oxidase activity of tumor cells.

This study is aimed at evaluating the inhibitory effects of the association of hematoporphyrin and ultrasound at variable intensities with a fixed frequency of 1.1MHz in tumor nodules. Specifically, the effects were studied both in solid and ascitic S180 tumors transplanted in mice by clinical, cytochemical and ultrastructural evaluation. The results indicated that the use of hematoporphyrin alone had no significant effect on destroying tumor cells. The ultrasound alone had little effect. Interestingly, the inhibition was much more effective when hematoporphyrin was combined with ultrasound. The inhibition was 3 times better than ultrasound alone and 8 times better than hematoporphyrin used alone. Our results also indicated that the changes on cell structure and cytochrome oxidation activity are important factors that could inhibit tumor cell growth and induce cell death. Apoptosis of tumor cells could be induced by hematoporphyrin. Our study investigated the killing mechanism on S180 tumor cells by using hematoporphyrin and low frequency ultrasound at cell, tissue and individual level.

Animals↗