Fixation of the quaternary structures of human adult haemoglobin by encapsulation in transparent porous silica gels.

We have used the sol-gel method to encapsulate oxy- and deoxy haemoglobins in transparent wet porous silica gels and fixed their original functional states with the retention of the reversible oxygenation properties as well as the intact spectroscopic properties. Haemoglobin originally encapsulated in aerobic gel binds oxygen non-cooperatively with very high affinity, corresponding to that for the last oxygen molecule binding to haemoglobin in solution. In contrast, haemoglobin originally encapsulated in anaerobic gel binds oxygen non-cooperatively with very low affinity, comparable to that for the first oxygen molecule binding to haemoglobin in solution. Furthermore, a detailed comparison of visible absorption spectra of deoxygenated haemoglobins originally encapsulated in aerobic and anaerobic gels indicates the retention of their original quaternary structures during the oxygenation or deoxygenation process. These results demonstrate that oxygen affinities of oxy- and deoxyhaemoglobins in solution can be satisfactorily fixed by encapsulation in wet porous silica gels, which presumably prevents the changes in the quaternary structures of haemoglobin. In addition, these results suggest a new capability of the sol-gel method to control the structural states of a variety of proteins, and further open up a new area of investigation of protein structure-function relationships.