Abstract
SP-40, 40 bound to β-endorphin via C-terminal non-opioid portion of β-endorphin as well as S-protein (vitronectin) bound. Beta-endorphin bound mainly to SP-40, 40, but not to S-protein, in the soluble membrane attack complex (SMAC, SC5b-9) of complement, because the results of autoradiography of the cross-linking experiment of SMAC with [125I]β-endorphin revealed only a typical band of SP-40, 40. The binding of SP-40, 40 to β-endorphin inhibited the binding of β-endorphin to its receptor of rat brain; thus SP-40, 40 might inhibit the biological action of β-endorphin.
