chrome oxidase content of tumors, both types of assay methods have not been used concurrently. Experiments described in this communication were designed to provide information about the cytochrome oxidase content of Morris hepatoma 3924A relative to normal, host, and fetal liver by using both the oxygen electrode enzymatic assay (jolarographic assay) and the spectral assay. As will be described...

Mixing ATP with soluble oxidized cytochrome c oxidase induces a spectral perturbation in the Soret region of the enzyme. This spectral perturbation is observed at ATP concentrations similar to those found to modulate the catalytic activity of cytochrome c oxidase [Malatesta, Antonini, Sarti & Brunori (1987) Biochem. J. 248, 161-165]. The process is reversible and corresponds to a simple binding...

In Papers I and II (1, 2) it was shown that basic phenylmercuric nitrate depressed a number of enzymes (cytochrome oxidase, succinoxidase, catalase, and several dehydrogenases), that it reacted with sulfhydryl groups, and that the depression of yeast respiration by the basic nitrate could be prevented by the presence of sulfhydryl-containing compounds, such as cysteine or homocysteine. These fi...

A simple spectroscopic method for determining the cytochrome c oxidase, cytochrome a, a3, content in tissue and mitochondria samples independent of myoglobin or blood contamination is described. Using tissue homogenates solubilized in Triton X-100, this assay relies on the selective reduction of mitochondrial cytochromes by the action of potassium cyanide. Monitoring the optical absorbance of t...

where the activity is determined by measuring the rate of oxidation of reduced cytochrome c. Smith (6, 7), Conrad (8, 9), Wainio (10-13) et ~2. have extensively investigated the effect of various factors on the cytochrome oxidase activity measured by System 2 with soluble and insoluble preparations of cytochrome oxidase, whereas among those (14-30) who have employed System 1, Slater (5), using ...

Analysis of the rotational mobility of spin-labeled bovine heart cytochrome c oxidase by saturation transfer electron paramagnetic resonance(ST-EPR) has recently demonstrated that this enzymic complex can be obtained as an aggregate of individual protein molecules which display little or no rotational mobility on the submillisecond time scale (1). Aggregation appears to occur as a result of pro...

Cytochrome bd oxidase operons from more than 50 species of bacteria contain a short gene encoding a small protein that ranges from ∼30 to 50 amino acids and is predicted to localize to the cell membrane. Although cytochrome bd oxidases have been studied for more than 70 years, little is known about the role of this small protein, denoted CydX, in oxidase activity. Here we report that Escherichi...

During the course of studies upon the quantitative cytoarchitectonic distribution of enzymes in mammalian cerebral cortex, the need arose for a rapid ultramicromethod for assay of cytochrome oxidase activity in samples of fresh tissue weighing as little as 50 y. The Cartesian diver micro respirometer has been used for manometric assay of cytochrome oxidase in unicellular organisms (1, 2) and in...

The recent discovery of small molecules targeting the cytochrome bc1 :aa3 in Mycobacterium tuberculosis triggered interest in the terminal respiratory oxidases for antituberculosis drug development. The mycobacterial cytochrome bc1 :aa3 consists of a menaquinone:cytochrome c reductase (bc1 ) and a cytochrome aa3 -type oxidase. The clinical-stage drug candidate Q203 interferes with the function ...