TC-99M-NEOGLYCOALBUMIN (NGA)-BINDING TO HUMAN HEPATIC BINDING-PROTEIN (HBP) INVITRO

1 Neoglycoalbumin (NGA) was synthesised by covalent coupling of 2‐imino‐ 2‐methoxyethyl‐1‐thio‐beta‐D‐galactopyranoside (IME‐thiogalactose) to the primary amino groups of human serum albumin (HSA). NGA was purified by ultrafiltration and size exclusion h.p.l.c. (SEC). 99mTc‐labelling was performed with and without SEC purification. 2 Estimation of 99mTc‐ NGA‐binding to human hepatic binding protein (HBP) revealed a complex behaviour indicating saturable high‐ and low‐affinity sites. The high‐ affinity binding capacity was 1.1 +/‐ 0.4 pmol mg‐1 human liver plasma membrane protein, the low‐affinity binding capacity was 6.2 +/‐ 1.8 pmol mg‐1 liver plasma membrane protein. The apparent equilibrium dissociation constants were 2.4 +/‐ 1.2 and 18.4 +/‐ 4.8 nM, respectively. 3 Specific binding of 99mTc‐NGA to human HBP in the presence of 100 microM unlabelled NGA, Ca++ and Mg++ at pH 7.5 and 37 degrees C reached 85 +/‐ 5% at equilibrium. The amount of ligand specifically bound increased with the amount of human liver membrane protein added. The concentration of unlabelled agonist necessary to displace 50% of ligand bound amounted to 100 nM. 1990 The British Pharmacological Society