Dependence of NO Recombination Dynamics in Horse Myoglobin on Solution Glycerol Content

The recombination dynamics of NO with horse heart myoglobin (Mb) following photolysis with a 570 nm excitation pulse were measured by time-resolved absorption with 250 fs temporal resolution. These measurements were carried out in room-temperature solutions in which the glycerol concentration was varied from 0 to 90% (w/v). The recombination of NO is nonsingle exponential in all cases, but becomes faster as the glycerol concentration is increased. The interpretation of these results is aided by a maximum entropy analysis to determine a distribution of rate processes consistent with the data. This analysis suggests that in buffer there are two dominant rate processes for NO recombination on the subnanosecond time scale, one at ≈10 ps and one at ≈200 ps. The dominant effect of increasing glycerol content is to increase the amplitude of the fast process, with no corresponding significant change in rate, and to decrease the amplitude of the slow process, but with a corresponding increase in rate. These result...