ISSN:
1432-1017
Keywords:
Transferrin
;
Metal-binding protein
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Physics
Notes:
Abstract The kinetics of binding of Cu (II), Tb (III) and Fe(III) to ovotransferrin have been investigated using the stopped-flow technique. Rate constants for the second-order reaction, k +, were determined by monitoring the absorbance change upon formation of the metal-transferrin complex in time range of milliseconds to seconds. The N and C sites appeared to bind a particular metal ion with the same rate; thus, average formation rate constants k + (average) were 2.4 × 104 M−1 s−1 and 8.3 × 104 M−1 S −1 for Cu (II) and Tb (III) respectively. Site preference (N site for Cu (II) and C site for Tb (III)) is then mainly due to the difference in dissociation rate constant for the metals. Fe (III) binding from Fe-nitrilotriacetate complex to apo-ovotransferrin was found to be more rapid, giving an average formation rate constant k + (average) of 5 × 105 M−1 s−1, which was followed by a slow increase in absorbance at 465 nm. This slow process has an apparent rate constant in the range 3 s−1 to 0.5 s−1, depending upon the degree of Fe (III) saturation. The variation in the rate of the second phase is thought to reflect the difference in the rate of a conformational change for monoferric and diferric ovotransferrins. Monoferric ovotransferrin changes its conformation more rapidly (3.4s−1) than diferric ovotransferrin (0.52 s−1). A further absorbance decrease was observed over a period of several minutes; this could be assigned to release of NTA from the complex, as suggested by Honda et al. (1980).
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00185414
