Human serum Cohn fraction IV (alpha-globulin [correction of globin] enriched) inhibits ligand binding at neurotransmitter receptors in human brain.

Human serum proteins are found in significant density in the neuropil in brains of demented individuals. The functional significance of these abnormally distributed proteins has been unknown. We now report that alpha-globulin-enriched fractions of human serum decrease the specific binding of [3H]spiroperidol at its binding sites in postmortem human frontal cortex and caudate. The substances in this serum fraction apparently exert their effect by a direct action on the binding site. Since [3H]spiroperidol labels serotoninergic and dopaminergic among other neurotransmitter receptors, these results suggest that components of human serum inhibit the binding of ligands at neurotransmitter receptors.