The reactions of hemopexin and liver fatty acid-binding protein (L-FABP) with aurothiomalate

We investigated whether gold(I) binds to hemopexin, Hx, a serum heme carrier with a molecular weight similar to that of serum albumin, or to L-FABP, a liver cytosolic heme- and fatty acid-binding protein whose molecular weight is similar to that of metallothionein. These proteins and, for comparison, similar concentrations of bovine albumin were incubated with sodium aurothiomalate and then fractionated by gel exclusion chromatography. At 16 μM of Hx and gold the ratio of gold bound to Hx was 0.30 ± 0.04. The corresponding ratio for albumin was 0.98 ± 0.04 per mercaptalbumin. Considering the much lower serum levels of Hx compared to albumin it is unlikely that Hx plays a role in serum gold binding and transport. L-FABP also binds gold: at 52 μM L-FABP and 108 μM gold, the gold to protein ratio was 0.55 ± 0.05. The corresponding ratio for albumin under identical conditions was 1.18 ± 0.08 per mercaptalbumin. L-FABP failed to bind zinc or cadmium, two other metals bound by metallothionein.