Effect of a covalently attached synergistic anion on chelator-mediated iron-release from ovotransferrin: additional evidence for two concurrent pathways.
The mechanism by which the iron-transport protein transferrin releases its iron in vivo is presently unclear. In vitro studies have implicated two concurrent chelator-mediated iron-release pathways: one which is hyperbolic in nature, involving a conformational change in the protein as a rate limiting step, and a second which has been proposed to be first-order in nature and to involve initial release of a synergistic anion. We have examined the effect that an affinity-label analog of the synergistic anion has on chelator-mediated iron-release from this protein. A covalently attached anion would inhibit iron-release via any pathway in which anion release is a prerequisite to iron release. The present investigation examined the effect that the covalently attached anion had on iron-release to pyrophosphate (PPi) and N, N-bis(phosphonomethyl)glycine (DPG), two chelators which are believed to utilize both pathways concurrently. Results show that when the affinity-label anion is utilized, strictly hyperbolic data are obtained, with similar observed kmax values. This is strong support for the hypothesis of a common, chelator-independent rate-limiting step for the one available pathway. These results also support strongly the hypothesis that synergistic anion removal is a prerequisite step to iron-release via the second pathway.
Bailey
C T
CT
Department of Biological and Chemical Sciences, Wells College, Aurora, New York 13026, USA.
Byrne
C
C
Chrispell
K
K
Molkenbur
C
C
Sackett
M
M
Reid
K
K
McCollum
K
K
Vibbard
D
D
Catelli
R
R
D000838:Anions; D002614:Chelating Agents / Q000737:chemistry*; D003207:Conalbumin / Q000737:chemistry*; D011756:Diphosphates / Q000737:chemistry*; D005998:Glycine / Q000031:analogs & derivatives* / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry*; D011487:Protein Conformation
D000838:Anions; D002614:Chelating Agents; D011756:Diphosphates; D009943:Organophosphorus Compounds; D003207:Conalbumin; C040598:glyphosphine; D007501:Iron; D005998:Glycine