Neutron protein crystallography. Evaluation of pKa of polar amino acid residues in proteins

The biological mechanism of the physiological function such as the enzymatic reaction is well understood by studying protonation states of the catalytic polar amino acid residues, which can be identified by neutron protein crystallography. It is proposed that the protonation states should be systematically discussed from the view point of the pKa values of the amino acid residues in proteins. Several examples of the protonation states of the catalytic residues determined by neutron protein crystallography, such as serine proteases (trypsin, elastase, thrombin, and achromobacter protease I), insulin, hen egg white lysozyme. RNase A, and HIV-1 protease were introduced and discussed on the basis of the pKa values. (author)