In ribonuclease T1,two surface-exposed acidic residues , GLu28,Asp29, are located near the carboxyl terminus of the alpha helix between residues 13 and 29. In case of Glu28Gln and Asp29Asn, there are a marginal stabilization of about 3.2kJ/mol. This stabilization is caused by unfavorable electrostatic interactions of Glus28 and Asp29 with the negative end of the helix dipole.

Structure of RNase T1 showing the residues of interests