Dehydration and crystallization of trehalose and sucrose glasses containing carbonmonoxy-myoglobin

We report a study wherein we contemporarily measured 1) the dehydration pro cess of trehalose or sucrose glasses embedding carbonmonoxy-myoglobin (MbCO ) and 2) the evolution of the A substates in saccharide-coated MbCO. Our re sults indicate that microcrystallization processes, sizeably different in t he two saccharides, take place during dehydration; moreover, the microcryst alline structure is maintained unless the dry samples are equilibrated with a humidity greater than or equal to 75% (greater than or equal to 60%) at 25 degrees C for the trehalose (sucrose) sample. The evolution of the param eters that characterize the A substates of MbCO indicates that 1) the effec ts of water withdrawal are analogous in samples dried in the presence or in -the absence of sugars, although much larger effects are observed in the sa mples without sugar; 2) the distribution of A substates is determined by th e overall matrix structure and not only by the sample water content; and 3) the population of A(0) substate (i.e., the substate currently put in relat ion with MbCO molecules having the distal histidine out of the heme pocket) is largely enhanced during the dehydration process. However, after rehumid ification its population is largely decreased with respect to the values ob tained, at similar water content, during the first dehydration run.