Apparent molecular weight of the substance P binding site in rat brain

Substance P (SP) binding sites in rat cerebral cortical membranes were specifically and covalently labelled by means of disuccinimidyl suberate (DSS), a bifunctional cross-linking reagent, to determine the apparent molecular weight of the SP binding site. Cross-linking of [3H]SP by 1 mM DSS to membranes revealed a specifically labelled single protein with an apparent molecular weight of 46,000, as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and gel filtration analyses. This labelling was inhibited by non-radioactive SP and was not changed by the presence or absence of GTPrS suggesting that the label was bound to the binding site of SP receptors.