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 Cpalmitic acid to probe the fatty acid binding pockets of DBP and ALB. We observed that N-ethyl-5-phenylisooxazolium-3′-sulfonate-ester (WRK ester) of 14 C-palmitic acid specifically labeled DBP; but p-nitrophenyl-and N-hydroxysuccinimidyl-esters failed to do so. However, p-nitrophenyl ester of 14 C-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.
KeywordsFatty acid-binding by vitamin D binding protein (DBP) and albumin (ALB); serum transport of fatty acids; affinity labeling analogs of palmitic acid; affinity labeling of fatty acid binding sites of DBP and ALB