The balance sheet of a hemoglobin. Thermodynamics of CO binding by hemoglobin trout I.
Explore the source record for details and available documents.
Animals↗
Biomedical subjects
A Colosimo
Publications and source records attributed to A Colosimo.
Oxygen "pulsed" cytochrome c oxidase: functional properties and catalytic relevance.
The kinetics of the reaction of cytochrome c with solubilized mammalian cytochrome c oxidase (ferrocytochrome c:oxygen oxidoreductase, EC 1.9.3.1) has been studied by a stopped-flow technique under two different experimental situations: (i) the completely oxidized enzyme (resting oxidase as obtained from the preparation) was mixed with reduced cytochrome c, and (ii) the completely reduced enzyme in the presence of reduced cytochrome c was exposed to a "pulse" of O2 (pulsed oxidase). Both sets of experiments were performed with either "limiting" or "excess" O2 (relative to oxidase), in the presence or absence of CO. Both the pre-steady-state events and the steady-state kinetics of cytochrome oxidase are found to be different in the two cases. This shows that the product of the reaction of fully reduced oxidase with O2 (pulsed oxidase) is functionally different from the oxidase as prepared (resting oxidase). These differences are interpreted with the assumption of a different rate of intramolecular electron transfer in the pulsed and resting oxidases. Implications of these experimental findings are discussed in the general framework of a tentative model for the catalytic cycle of the oxidase.
Animals↗
Electron transfer between soluble and immobilized mammalian cytochrome c. Equilibrium and kinetic studies on immobilized cytochrome c.
Horse heart cytochrome c was covalently bound to Sepharose 4B and its redox properties were measured under various experimental conditions. The equilibrium constant for the electron exchange between the oxidized and the reduced form of cytochrome c when one of the two forms was in the semi-solid state and the other one in solution was close to 1. Matrix-bound ferrocytochrome c is very stable to autoxidation and is not oxidized by O2 even in the presence of mammalian cytochrome oxidase. Oxidation occurs if catalytic amounts of soluble cytochrome c are added to the reaction mixture. The rate of oxidation of matrix-bound ferrocytochrome c in the presence of cytochrome oxidase and catalytic amounts of soluble cytochrome c may be correlated with the rate of electron transfer between soluble and matrix-bound cytochrome c. This rate is more than two orders of magnitude lower than that reported for the homonuclear (between identical species) electron transfer in solution.
Animals↗
Pulsed cytochrome c oxidase.
The identification of two functionally distinct states, called pulsed and resting, has led to a number of investigations on the conformational variants of the enzyme. However, the catalytic properties of cytochrome oxidase may depend on a number of experimental conditions related to the solvent as well as to the protocol followed to determine the turnover number of the enzyme. This paper reports results which illustrate that the steady-state differences between pulsed and resting oxidase may, or may not, be detected depending on experimental conditions.
Animals↗
Stopped-flow studies of cytochrome oxidase reconstituted into liposomes: proton pumping and control of activity.
The transient kinetics of proton pumping and the electron transfer properties of cytochrome oxidase inserted into small unilamellar vesicles have been investigated by stopped-flow spectrophotometry. In the presence of valinomycin, proton pumping and cytochrome c oxidation by cytochrome oxidase are synchronous up to rate constants of approximately 9 sec-1. Moreover, the enzyme depleted of subunit III ("three-less oxidase") was also shown to pump protons, although with a significantly smaller stoichiometry. Thus, subunit III is not the only (or even the main) proton channel, although it may be involved in the regulation of activity. The kinetics of cytochrome c oxidation by COV in the absence and in the presence of ionophores have been investigated. Analysis of the time course of the process in the transient and steady state phases indicates that the onset of control by the electrochemical gradient follows the transfer of four electrons, i.e., one complete turnover of the oxidase. Two possible alternative interpretations for the control of the turnover phase are presented and discussed.
Animals↗
GCG Stacks: a friendly interface for the GCG programs.
A 'PLUS' stack which provides a friendly user interface for the GCG suite of programs is presented. The interface takes advantage of the whole set of programming tools available in a graphical and object-oriented environment and its major features include: (i) an efficient management of the on-line help documents, and (ii) a flexible editor for macrocommands. The former facilitates finding specific information in the huge documentation bundled with the GCG suite, and the latter is useful whenever several GCG programs must be run in sequence with automatic piping of the intermediate results.
Database Management Systems↗