Aluminium transport in blood serum. Binding of aluminium by human transferrin in the presence of human albumin and citrate.
The binding of Al3+ by human serum transferrin has been investigated by u.v.-visible difference spectroscopy. In the presence of 25 mM-HCO3- at pH 7.4, the apparent association constants were found to be 1.69 x 10(12) M-1 and 5.36 x 10(11) M-1. These association constants are pH-dependent, reducing with both increasing and decreasing pH. The apparent pKa values were found to be 6.7 and 8.2. Competitive assays of binding of Al3+ to transferrin in the presence of citrate and human serum albumin at molar ratios corresponding to those found in normal plasma showed that a considerable amount of Al3+ was not bound to transferrin. Taking a concentration of 5 microM as a typical value observed for the plasma of patients on haemodialysis [Harris & Sheldon (1990) Inorg. Chem. 29, 119-124] the competitive binding assay indicate that approximately 60% of it is bound to transferrin, approximately 34% to albumin and the remainder to citrate. These results therefore suggest that, although transferrin at pH 7.4 is the major Al(3+)-binding component of plasma, an appreciable amount of Al3+ present in patients on haemodialysis may be bound to albumin.
Fatemi
S J
SJ
Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences, University of East Anglia, Norwich, U.K.
Kadir
F H
FH
Moore
G R
GR
D000535:Aluminum / Q000097:blood*; D001667:Binding, Competitive; D001692:Biological Transport; D002951:Citrates / Q000378:metabolism*; D019343:Citric Acid; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D012709:Serum Albumin / Q000378:metabolism*; D014168:Transferrin / Q000378:metabolism*
D002951:Citrates; D012709:Serum Albumin; D014168:Transferrin; D019343:Citric Acid; D000535:Aluminum