Oxygen dependence of redox state of copper in cytochrome oxidase in vitro.
To obtain quantitative information about tissue oxygenation from near-infrared signals, the oxygen dependencies of the redox states of both heme a+a3 and copper in cytochrome oxidase of isolated mitochondria were determined at low oxygen concentrations (10(-6)-10(-9) M) using leghemoglobin as an oxygen indicator. The maximum absorbance changes caused by the aerobic-anaerobic transition measured at 830-760 nm of copper in state 3, state 4, and the uncoupled state were 10, 17, and 5% of those at 605-620 nm of heme a+a3, respectively. Thus the relative absorbance ratio of copper to heme a+a3 could be used as a sensitive indicator for the mitochondrial energy state. The oxygen concentrations required for the half-maximal reduction of heme a+a3 varied with the energy state and the respiratory rate and were 7.8 x 10(-8) and 1.6 x 10(-7) M in state 4 and state 3, respectively. In contrast, that of copper was 7.5 x 10(-8) M and was independent of both the energy state and the respiratory rate. The relationship between the percent oxidation of heme a+a3 and copper in the aerobic-anaerobic transition did not show a straight-line relationship. This was referred to as the difference in oxygen affinity between these two chromophores. The deviation from the straight line was larger in state 3 than in state 4.(ABSTRACT TRUNCATED AT 250 WORDS)
Hoshi
Y
Y
Research Institute for Electronic Science, Hokkaido University, Sapporo, Japan.
Hazeki
O
O
Tamura
M
M
D000332:Aerobiosis; D000693:Anaerobiosis; D000818:Animals; D003300:Copper / Q000378:metabolism*; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006418:Heme / Q000031:analogs & derivatives / Q000378:metabolism; D066298:In Vitro Techniques; D007874:Leghemoglobin / Q000378:metabolism; D008929:Mitochondria, Heart / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D011817:Rabbits; D013055:Spectrophotometry, Infrared
D007874:Leghemoglobin; C027728:heme a; D006418:Heme; D003300:Copper; D003576:Electron Transport Complex IV; D010100:Oxygen