Open AccessImplication of Two Histidines in Transition‐Metal Binding in Concanavalin A
Author(s) -
Gachelin Gabriel,
Goldstein Leon,
Hofnung Daniel,
Kalb A. Joseph
Publication year - 1972
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1972.tb02082.x
Subject(s) - concanavalin a , chemistry , histidine , transition metal , metal , metal ions in aqueous solution , binding site , inorganic chemistry , titration , potentiometric titration , ion , organic chemistry , biochemistry , amino acid , catalysis , in vitro
We have performed potentiometric titrations and chemical modifications of demetallized concanavalin A and of the Ni 2+ concavalin A complex. Two protons are released upon binding of one Ni 2+ ion per concanavalin A subunit. The pH‐dependence of proton release indicates that two ionizable groups with p K a 6.8 are ligands for binding of the transition‐metal ion. Ethoxyformylation of histidines causes the destruction of the transition‐metal‐binding site unless it is occupied by a transition‐metal ion. For each transition‐metal site thus protected two otherwise ethoxyformylated histidines are rendered inert to the chemical modification. On photooxidation in the presence of rose bengal, protection of histidines and of the transition‐metal‐binding capacity was also observed to occur when Ni 2+ ions were present. Two histidine residues in concanavalin A are, therefore, very likely metal‐ion ligands in the binding site.