Spectroscopic and functional properties of subunit III-depleted cytochrome oxidase

Beef heart cytochrome c oxidase has been depleted of subunit I11 by treatment with chymotrypsin. The removal of subunit 111 has been evaluated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and gel fluorography of preparations of the oxidase labeled with [14C]dicyclohexylcarbodiimide prior to proteolysis. Removal of subunit I11 resulted in a perturbation of the visible spectrum of reduced cytochrome oxidase. Subunit III-depleted oxidase is spectroscopically very similar to the oxidase from Paracoccus denitrificans. When reconstituted into liposomes, the depleted enzyme still pumped protons in response to a pulse of reduced cytochrome c. The H+/e- stoichiometry averaged 0.5. Redox-linked proton translocation could be observed only when respiratory control ratios were higher than 3 and the reductant pulse was of a magnitude that allowed for no more than 5 turnovers of the oxidase

Valence photoelectron spectroscopy of N-2 and CO: Recoil-induced rotational excitation, relative intensities, and atomic orbital composition of molecular orbitals

Recoil-induced rotational excitation accompanying photoionization has been measured for the X, A, and B states of N-2(+) and CO+ over a range of photon energies from 60 to 900 eV. The mean recoil excitation increases linearly with the kinetic energy of the photoelectron, with slopes ranging from 0.73 x 10(-5) to 1.40 x 10(-5). These slopes are generally (but not completely) in accord with a simple model that treats the electrons as if they were emitted from isolated atoms. This treatment takes into account the atom from which the electron is emitted, the molecular-frame angular distribution of the electron, and the dependence of the photoelectron cross section on photon energy, on atomic identity, and on the type of atomic orbital from which the electron is ejected. These measurements thus provide a tool for investigating the atomic orbital composition of the molecular orbitals. Additional insight into this composition is obtained from the relative intensities of the various photolines in the spectrum and their variation with photon energy. Although there are some discrepancies between the predictions of the model and the observations, many of these can be understood qualitatively from a comparison of atomic and molecular wavefunctions. A quantum-mechanical treatment of recoil-induced excitation predicts an oscillatory variation with photon energy of the excitation. However, the predicted oscillations are small compared with the uncertainties in the data, and, as a result, the currently available results cannot provide confirmation of the quantum-mechanical theory. (C) 2010 American Institute of Physics. [doi:10.1063/1.3503658