Fatty acid-binding site environments of serum vitamin D-binding protein and albumin are different

Vitamin D-binding protein (DBP) and albumin (ALB) are abundant serum proteins and both possess high-affinity binding for saturated and unsaturated fatty acids. However, certain differences exist. We surmised that in cases where serum albumin level is low, DBP presumably can act as a transporter of fatty acids. To explore this possibility we synthesized several alkylating derivatives of 14 C-palmitic acid to probe the fatty acid-binding pockets of DBP and ALB. We observed that N-ethyl-5-phenylisooxzLzolium-3'-sulfonate-ester (WRX-ester) of C-14-palmitic acid specifically labeled DBP; but p-nitrophenyl- and N-hydroxysuccinimidyl-esters failed to do so. However, p-nitrophenyl ester of C-14-palmitic acid specifically labeled bovine ALB, indicating that the micro-environment of the fatty acid-binding domains of DBP and ALB may be different; and DBP may not replace ALB as a transporter of fatty acids. (C) 2008 Elsevier Inc. All rights reserved.