Electrostatic stabilization in sperm whale and harbor seal myoglobins. Identification of groups primarily responsible for changes in anchoring of the A helix.

• Main Authors: Gurd, F R, Friend, S H, Rothgeb, T M, Gurd, R S, Scouloudi, H
• Format: Text
• Language: English
• Published: 1980
• Subjects: Research Article; Kirkwood; harbor seal; Sperm whale
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1327257; http://www.ncbi.nlm.nih.gov/pubmed/7248465

The compact, largely helical structure of sperm whale and harbor seal myoglobins undergoes an abrupt one-step transition between pH 4.5 and 3.5 as monitored by changes in either the heme Soret band absorbance or circular dichroism probes of secondary structure, for which a modified Tanford-Kirkwood theory provides identification of certain dominant electrostatic interactions responsible for the loss of stability. A similar treatment permits identification of the electrostatic interactions primarily responsible for a process in which the anchoring of the A helix to other parts of the molecule is weakened. This process is detected with both myoglobins, in a pH range approximately 1 unit higher than the onset of the overall unfolding process, through changes in the circular dichroic spectra near 295 nm which correspond to the L1 O-O band of the only two tryptophan residues in these proteins, residues 7 and 14. In each case protonation of certain sites in neighboring parts of the molecule can be identified as producing destabilizing interactions with components of the A helix, particularly with lysine 6.