Kinetics of association of carbon monoxide with haemoglobin at low temperature

Nanosecond laser photolysis of aqueous carbon monoxy- and oxyhaemoglobin

The spectra have been measured of the transient species and the final level of absorption observed in nanosecond laser photolysis of aqueous carbon monoxy- and oxyhaemoglobin. These show that the transient absorption change can be interpreted as being due to an ultrafast ligand recombination following the photolysis. The spectra do not support the earlier interpretation (Alpert, B., Banerjee, R. and Lindqvist, L. (1974) Proc. Natl. Acad. Sci. U.S. 71, 558--562) that this was due to a tertiary structural change of the protein.

New trends in cryoenzymology: I.-Supercooled aqueous solutions

A water in oil emulsion technique is proposed to investigate enzyme catalyzed reactions at sub-zero temperatures in the supercooled liquid state to avoid some reversible effects of the usual cosolvents on kinetics. Some results are listed: potentialities and technical problems of the procedure are discussed.

Recombination of carbon monoxide with hemoglobin after flash photolysis of the carboxyderivative in mixed solvents at subzero temperature

The kinetics of recombination of carbon monoxide to hemoglobin produced by total flash photolysis of its carboxyderivative are studied at low temperatures (down to --55 degrees C) in mixed hydroalcoholic solvents. The rates are found to be different in two solvents used, namely ethylene glycol/buffer and methanol/buffer; for the former, the rates at subzero temperatures are simply explained by cooling and are consistent with the activation energy as measured in aqueous solution, while those in methanol/buffer show evidence of a specific solvent effect. Values are reported for the rate constants and activation energies in the two solvents.

Temporal resolution of individual steps in an enzymic reaction at low temperature

Media are described which make it possible to study mechanisms of enzyme action at low temperature. The applicability of techniques developed are illustrated by results obtained on formation kinetics of complexes produced by the interaction of horseradish peroxidase with hydrogen peroxide. It is shown that the various steps in the time course of the reaction can be readily resolved with isolation of each intermediate in concentrations sufficient to permit rate studies between consecutive steps. The potential of the method for elaboration of enzyme mechanisms is discussed.