Open AccesspH‐induced structural changes in human serum apotransferrin p K a values of histidine residues and N‐terminal amino group determined by 1 H‐NMR spectroscopy
Author(s) -
KUBAL Gina,
SADLER Peter J.,
TUCKER Alan
Publication year - 1994
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1994.tb18679.x
Subject(s) - histidine , chemistry , nuclear magnetic resonance spectroscopy , spectroscopy , crystallography , stereochemistry , amino acid , biochemistry , physics , quantum mechanics
The binding of apotransferrin (80 kDa) to the transferrin receptor is known to be highly pH‐dependent. We have investigated pH‐induced structural changes in human serum apotransferrin over the pH * (meter reading in D 2 O solutions) range 2.5–11 using 1 H‐NMR spectroscopy. The p K a values of 14 (possibly 15) of the 19 His residues in the protein have been determined as well as that of the terminal amino group (Val1, 7.75). About eight His residues deprotonate when the pH * is raised from the endosomal value of about 5.5 to the blood plasma value (7.4). Four His residues have p K a < 6. Sharp discontinuities in the His titration curves were observed below pH 4.3 and at pH 3.5 molten globule states were detected.