BUMETANIDE BINDING TO NORMAL ALBUMINS AND TO ALBUMIN IN RENAL-FAILURE

Binding of bumetanide, a loop diuretic, to partially purified albumins from renal failure patients (RF-HA), and healthy subjects (N-HA), hum an serum albumin (HSA) and defatted-HSA (D-HSA), was studied with equi librium dialysis at a constant albumin concentration and various ligan d concentrations. Binding parameters (n and K) were estimated from Sca tchard plots and with a non-linear two-binding site model computer pro gram, assuming two classes of independent sites. The binding capacitie s (n1K1) decreased in the order N-HA>RF-HA>D-HSA > HSA. Computer estim ates of K1 for the partially purified albumin preparations were not ma rkedly different. However, the graphical estimate of K1 for N-HA was g reater than that for RF-HA. When the degree of binding (r) was plotted as a function of the logarithm of the free bumetanide concentration, an asymptotic plateau was not observed, indicating that the protein bi nding sites were not saturated. Consequently, the calculated binding e stimates may not adequately describe the binding of bumetanide.