RESUMO
The problem of evaluating dissipative effects in macroscopic quantum tunneling is re-examined for the case of Josephson junctions, with the adoption of an alternative way with respect to several previously proposed and, in some cases, contradictory approaches. The system, which consists of a junction coupled to a transmission line, is analyzed both analytically and numerically. A test of the theoretical model, as compared to the experimental results available, is performed in accordance with a criterion based on a shortening of the traversal time.
RESUMO
The ubiquinol-cytochrome c oxidoreductase (bc1 complex, EC 1.10.2.2) has been isolated from the heart mitochondria of beef, chicken, turkey, duck and tuna with an identical procedure. The polypeptide composition of the different complexes, compared using SDS-polyacrylamide gel electrophoresis, shows that the three subunits carrying the prosthetic groups of the enzyme are highly conserved in all species. Also the large subunits I and II (core proteins) and band VI appear to be conserved in structure, while subunits VII and VIIa show a most remarkable structural variation in the various complexes. The steady-state ubiquinol-cytochrome c reductase analysis of the active enzymes indicates that all the bc1 complexes follow essentially a ping-pong mechanism, with the cytochrome c substrate displaying a partial competitive inhibition vs the ubiquinol substrate. The cytochrome c specificity of the reductase activity clearly is different in the various bc1 complexes, whereas the quinol specificity appears to be identical in all the enzymes.
