INVOLVEMENT OF TYROSYL RESIDUE(S) IN BINDING OF ENDOTHELIN AND SARAFOTOXIN TO THEIR RECEPTORS IN RAT-BRAIN AND HEART

The possible involvement of tyrosyl residue(s) in the binding of endothelins and sarafotoxins to their receptors was examined by the use of tetranitromethane. Incubation of rat cerebellar, hypothalamic. caudate putamen and atrial membranes with the reagent (100-mu-M, pH 8.1, 20 min) was accompanied by a decrease in their capacity to bind endothelins and sarafotoxin. Experiments employing nitration at different pH values (6.0 vs. 8.1) and studies on the effect of dithiothreitol on the nitrated preparations indicated that the modified residue(s) is most probably a tyrosyl and not a cysteinyl residue, and that there is no oligomerization of the receptors. These data are discussed in relation to the structural data recently obtained by cloning and expression of the endothelin/sarafotoxin receptors.