Description_x000D_ General description_x000D_ Retinol binding protein 4 (RBP4; RBP) is a 21 kDa secreted protein, a member of the lipocalin family and is known as the primary transporter of retinol (vitamin A) to tissues. A recent report revealed RBP4 as an adipokine linking glucose transporter 4 (GLUT4) suppression in adipose tissue to insulin. Elevated human and mouse serum RBP4 levels are associated with insulin resistance and its severity, obesity, and certain components of metabolic syndrome. Furthermore, human serum RBP4 levels are closely related to renal function._x000D_ Physical form_x000D_ 0.2 μm-filtered solution in 55 mM TRIS-Cl, pH 8.2 containing 150 mM NaCl. .