INTERACTIONS OF RETINOL WITH BINDING-PROTEINS - STUDIES WITH RETINOL-BINDING PROTEIN AND WITH TRANSTHYRETIN

被引:87
作者
NOY, N
SLOSBERG, E
SCARLATA, S
机构
[1] CORNELL UNIV,MED CTR,COLL MED,DEPT MED,NEW YORK,NY 10021
[2] SUNY STONY BROOK,DEPT PHYSIOL & BIOPHYS,STONY BROOK,NY 11794
关键词
D O I
10.1021/bi00160a023
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The interactions within the molecular complex in which retinol circulates in blood were studied. To monitor binding between retinol-binding protein (RBP) and transthyretin (TTR), TTR was labeled with a long-lived fluorescence probe (pyrene). Changes in the rotational volume of TTR following its association with RBP were monitored by fluorescence anisotropy of the probe. Titration of TTR with holo-RBP revealed the presence of 1.5 binding sites characterized by a dissociation constant K(d) = 0.07 muM. At 0.15 M NaCl, binding of RBP to TTR showed an absolute requirement for the native ligand, retinol. At higher ionic strength (0.5 M NaCl), RBP complexed with retinal also bound to TTR with high affinity (K(d) = 0. 134 muM). RBP containing retinoic acid did not bind to TTR even at the high salt concentration. The data suggest that the TTR binding site on RBP is in close proximity to the retinoid binding site and that the head group of retinoic acid, when bound to RBP, presents steric hindrance for the interactions with TTR. The implications of the data for selectivity in retinoid transport in the circulation are discussed. The kinetics of the steps leading to complete dissociation of the retinol-RBP-TTR complex was also studied. The first step of this process was dissociation of retinol, which had a rate constant of 0.06/min. Following loss of retinol, the two proteins dissociate. The rate of dissociation is slow (k=0.055/h), however, indicating that the complex apo-RBP-TTR will be an important factor in regulating serum levels of retinol.
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页码:11118 / 11124
页数:7
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