Kinetics of hemoglobin-carbon monoxide reactions measured with a superconducting magnetometer: a new method for fast reactions in solution.

A new technique for measuring fast reactions in solution has been demonstrated. The changes in magnetic susceptibility during the recombination reaction of human hemoglobin with carbon monoxide after flash photolysis have been measured with a new high-sensitivity instrument using cryogenic technology. The rate constants determined at 20 degrees (pH 7.3) are in excellent agreement with those obtained by photometric techniques [Gray, R.D. (1974) J. Biol. Chem. 249, 2879-2885]. A unique capability of this new method is the determination of the magnetic susceptibilities of short-lived reaction intermediates. The magnetic moment of the intermediate species Hb4(CO)3 was found to be 4.9+/-0.1 muB in 0.1 M phosphate buffer by partial photolysis experiments. This value agrees with the predictions of two-state allosteric models of cooperativity in hemoglobin. Possible applications and improvements in this technique are discussed.