Structure of an Exophthalmos-producing Thyrotropin by Partial Pepsin Digestion
نویسنده
چکیده
Previously reported experiments (Winand, R. J., and Kohn, L. D. (1970) J. Biol. Chem. 245, 967-975; Kohn, L. D., and Winand, R. J. (1971) J. Biol. Chem. 246, 6570-6575) have demonstrated that partial pepsin digestion of bovine thyrotropin preparation yields a fragment of the thyrotropin molecule which is exophthalmogenic but has negligible or no thyroid-stimulating activity. In the present report this exophthalmogenic derivative of the thyrotropin molecule is shown to contain two major polypeptide components with approximate molecular weights of 14,000 and 6,000. Amino acid analyses, carbohydrate analyses, and tryptic digestion experiments indicate that this exophthalmogenic factor is composed of an intact or nearly intact /3 subunit of thyrotropin and an NH,-terminal fragment of the LY subunit of thyrotropin. Neither polypeptide component of the exophthalmogenic factor has the in uivo exophthalmogenic activity of the intact structure. In uitro the intact exophthalmogenic derivative of the thyrotropin molecule can bind to the thyrotropin receptor on thyroid membranes less efficiently than thyrotropin but significantly better than either its own polypeptide components or the (Y or /3 subunits of thyrotropin. The exophthalmogenic factor and its parent thyrotropin molecule can stimulate adenylate cyclase activity in retro-orbital tissue membranes from guinea pigs, a mammalian model of exophthalmos; its polypeptide components have little or no such activity.
منابع مشابه
Relationship of thyrotropin to exophthalmos-producing substance. Formation of an exophthalmos-producing substance by pepsin digestion of pituitary glycoproteins containing both thyrotropic and exophthalmogenic activity.
Homogeneous bovine pituitary glycoproteins with both thyrotropic and exophthalmogenic activity have been subjected to limited proteolysis by pepsin. One fraction lost 90 % of its thyrotropin action, but only 15 % of its exophthalmogenic activity, when incubated with a 1% weight ratio of pepsin at pH 2.2 and at 3’7”. Analytical disc gel analyses showed that the decrease in thyrotropin activity c...
متن کاملExperimental exophthalmos. Binding of thyrotropin and an exophthalmogenic factor derived from thyrotropin to retro-orbital tissue plasma membranes.
Biologically active preparations of 125I-thyrotropin, [3H]thyrotropin, and the [3H]exophthalmogenic factor derived from thyrotropin by partial pepsin digestion have been used to study the binding properties of the thyrotropin receptor on guinea pig retro-orbital tissue plasma membranes. In regard to the optimal conditions of binding, pH, buffer, salt concentrations, and temperature, these prope...
متن کاملStimulation of adenylate cyclase activity in retro-orbital tissue membranes by thyrotropin and an exophthalmogenic factor derived from thyrotropin.
Retro-orbital tissue membranes have been shown to have adenylate cyclase activity which can be stimulated by thyrotropin and by an exophthalmogenic factor derived from the thyrotropin molecule by partial pepsin digestion. This stimulable activity is maximal after 15 min and is optimal in the presence of 3 mM magnesium and 1.5 mM ATP. Calcium salts are exquisitely inhibitory to the hormonal stim...
متن کاملBinding of Thyrotropin and an Exophthalmogenic Factor Derived from Thyrotropin to Retro-orbital Tissue Plasma Membranes
Biologically active preparations of ‘*%thyrotropin, [3H]thyrotropin, and the [3H]exophthalmogenic factor derived from thyrotropin by partial pepsin digestion have been used to study the binding properties of the thyrotropin receptor on guinea pig retro-orbital tissue plasma membranes. In regard to the optimal conditions of binding, pH, buffer, salt concentrations, and temperature, these propert...
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تاریخ انتشار 2002