Kinetic trapping of oxygen in cell respiration

CELL respiration in eukaryotes is catalysed by the mitochondrial enzyme cytochrome c oxidase. In bacteria there are many variants of this enzyme, all of which have a binuclear haem iron–copper centre at which O2 reduction occurs, and a low-spin haem, which serves as the immediate electron donor to this centre1. It is essential that the components of the cell respiratory system have a high affinity for oxygen because of the low concentrations of dissolved O2 in the tissues; however, the binding of O2 to the respiratory haem–copper oxidases is very weak2,3. This paradox has been attributed to kinetic trapping during fast reactions of O2 bound within the enzyme's binuclear haem iron–copper centre2. Our earlier work3 indicated that electron transfer from the low-spin haem to the oxygen-bound binuclear centre may be necessary for such kinetic oxygen trapping. Here we show that a specific decrease of this haem–haem electron transfer rate in the respiratory haem–copper oxidase from Escherichia coli leads to a corresponding decrease in the enzyme's operational steady-state affinity for O2. This demonstrates directly that fast electron transfer between the haem groups is a key process in achieving the high affinity for oxygen in cell respiration.

CO2 Isotope Analyzer

The CO2 Isotope Analyzer is an autonomous instrument capable of measuring the 13C/12C ratio in ambient carbon dioxide with better than 0.25‰ repeatability (for an integration time of 60 seconds) and without the need for costly consumables. This is possible because the instrument itself is built around conventional telecommunications-grade diode lasers that operate in the near-infrared spectral region. In addition, since the measurement strategy is based on high-resolution direct-absorption spectroscopy (see www.LGRinc.com, Theory Section), the instrument is not affected by other atmospheric gases or by changes in ambient atmospheric pressure. Thus the need for regular calibration with expensive reference gases is also significantly reduced compared with traditional analytical instruments.The instrument includes an internal computer that can store data practically indefinitely on its hard drive (for applications requiring unattended long-term standalone operation), and send real-time data to a data logger through its analog, digital (RS232), and Ethernet outputs.