Fatty acid binding protein (FABP) modulates prostaglandin E binding to rat epididymal adipocyte membrane similarly to albumin

Albumin enhances prostaglandin E₂ (PGE₂) binding to isolated epididymal adipocyte membrane and also binds PGE₂ with low affinity. On the other hand, S-100, ovalbumin and albumin-stearate failed to bind PGE₂, as shown by ultrafiltration, and also failed to enhance PGE₂ binding to the isolated adipocyte membranes. These results suggested that albumin enhances PGE₂ binding possibly by serving as a carrier for the prostaglandin molecules. 3 mM warfarin or 1 mM phenylbutazone inhibited PGE₂ binding to albumin by 70% and 95%, respectively, but both drugs failed to affect the enhancement of PGE₂ binding to the isolated adipocyte membrane in the presence of albumin. These results exclude the possibility that PGE₂ bound to albumin is more accessible to the prostaglandin receptor than free PGE₂ in solution. Finally it is shown that fatty acid binding protein (FABP), a cytosolic protein which binds specifically PGE₁ but not PGE₂, enhances PGE₁ and PGE₂ binding to isolated adipocyte membranes similarly to albumin. The physiological implications of these findings are discussed.