Interactions of bovine neurophysins with neurohypophyseal hormones. On the role of tyrosine-49.
Reaction of tetranitromethane with the lone tyrosine residue of bovine neurophysin I and II, tyrosine-49, gave nitro derivatives of these proteins which were obtained in a highly purified form by preparative electrophoresis. Equilibrium dialysis experiments indicated clearly that oxytocin binding remained essentially unaffected by the chemical modification of tyrosine-49. However, in the case of (8-lysine)vasopressin, the nitrated protein was found to bind only 1 hormone molecule in contrast to the 2 vasopressin molecules bound by the native protein. Ultraviolet absorption difference spectroscopy measurements between 250 nm and 300 nm indicated that upon binding of (2-phenylalanine, 8-lysine)vasopressin, tyrosine-49 of native neurophysin undergoes a change of microenvironment from less to more polar surroundings. Studies of the nitrotyrosyl-49 chromophore of neurophysin by ab sorption spectroscopy in the absence and presence of oxytocin or (8-lysine)vasopressin confirmed this finding. Since dimethylsulfoxide solvent perturbation studies suggested that in the Cys(Me)-Phe-Ile-NH2-neurophysin I complex, tyrosine-49 is more exposed to solvent than in neurophysin I alone, it is concluded that this residue is unmasked by conformational changes upon complex formation.
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002417:Cattle; D003956:Dialysis; D004591:Electrophoresis, Polyacrylamide Gel; D008236:Lypressin / Q000378:metabolism*; D009481:Neurophysins / Q000378:metabolism*; D009574:Nitro Compounds; D010121:Oxytocin / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism; D011485:Protein Binding; D013056:Spectrophotometry, Ultraviolet; D013774:Tetranitromethane / Q000378:metabolism; D014316:Tritium; D014443:Tyrosine / Q000378:metabolism*; D014667:Vasopressins / Q000031:analogs & derivatives*
D000596:Amino Acids; D009481:Neurophysins; D009574:Nitro Compounds; D014316:Tritium; D014667:Vasopressins; D014443:Tyrosine; D010121:Oxytocin; D008236:Lypressin; D013774:Tetranitromethane