Student Theses and Dissertations
Date of Award
1962
Document Type
Thesis
Degree Name
Doctor of Philosophy (PhD)
Thesis Advisor
Philip Siekevitz
Keywords
oxytocin inactivation, toad bladder enzyme, cystinyl-peptide bond, hormone regulation, enzyme kinetics, Bufo marinus
Abstract
The urinary bladder of the toad, Bufo marinus, was homogenized and the particle-free supernatant fraction prepared. Incubation of this fraction with the hormones, oxytocin, arginine vasopressin, lysine vasopressin, and oxytocin ring amide caused their inactivation. The decrease in hormone activity was roughly exponential with the time of incubation. The hormone inactivating activity of the supernatant fraction was decreased by treatment with N-ethylmaleimide, by heating to 50° C for 5 minutes, and by cold storage at -20° C. The decrease in activity due to cold storage, but not that due to either of the other two treatments, was reversed by the addition of 1 mM cysteine shortly before incubation with hormone. Ammonium sulfate fractions of the supernatant fraction were prepared and tested for oxytocin inactivating activity. The fraction precipitating between 50 and 70% saturation was the most active. In the presence of cysteine, it inactivated 35 mμM oxytocin per mg protein per hour. In the absence of cysteine, the same fraction, after being passed through Sephadex G-25, inactivated 16 mμM oxytocin per mg protein per hour. The incubation mixtures of the most active ammonium sulfate fraction and oxytocin (no cysteine) was examined chromatographically, following TCA precipitation of the protein. After an incubation of 4 hours at 30° C no oxytocin could be detected on a paper chromatogram. Moreover, there was an increase in ninhydrin positive material as compared with the controls. The same incubation mixture was subjected to performic acid oxidation and then chromatographed. A dense spot corresponding to cysteic acid was obtained. This was interpreted as indicating that the N-terminal half-cystinyl-tyrosine bond of oxytocin had been split. The ammonium sulfate fractions were also tested for their splitting of the synthetic substrate L-cystine-di-β-naphthylamide (CDNA). This substrate, like oxytocin, contains a N-terminal cystinyl-peptide bond. Again the most active fraction was that precipitating between 50 and 70% saturation. In the presence of 1 mM cysteine, it liberated 70 mμM β-naphthylamine per mg protein per hour. This was about twice its rate of inactivation of oxytocin. This CDNAase activity was increased by cysteine and decreased by N-ethylmaleimide, iodoacetic acid, and oxidized glutathione. It was decreased also by heating to 50° C for a few minutes. It appeared on the basis of these results that CDNA and oxytocin were being attacked by the same enzyme. The ammonium sulfate fractions were tested for their splitting of L-leucine-β-naphthylamide (LNA). The pattern of the fractionation of the LNAase activity was the same as that of the CDNAase activity. By a number of criteria, it appeared that LNA and CDNA were being split by the same enzyme. On the basis of these results it was concluded that a hormone inactivating enzyme is present in the toad bladder which splits N-terminal cystinyl-peptide bonds and also N-terminal leucinyl-peptide bonds. It was compared with pregnancy serum oxytocinase and leucine aminopeptidase and was found to be different than either of these. The inactivation of oxytocin by the intact toad bladder was then tested. It was found that the effect of a dose of oxytocin on the water permeability of the bladder decreased with time, but that this decrease was not due simply to inactivation of the hormone. The bladder released into its serosal bath an inhibitor of the action of hormone, and it was inferred that this inhibitor was released in response to the hormone. A theoretical model of hormone action was constructed in which the hormone is inactivated in the epithelial cells of the bladder, and the product of this inactivation acts as a competitive inhibitor of the hormone in its attachment to a receptor site. The solution of the mathematical expressions of this model fit the experimental data of the time course of the action of the hormone, over the entire concentration range. In fitting the theoretical solution to the experimental data, six constants were obtained, four of which are probably characteristic of the hormone species. The implications of this kind of kinetic analysis for the understanding of hormone-structure-function relationships were discussed. It was suggested that a possible physiological role for the inactivating enzyme, found in the first part of this work, is to convert the hormone to an inactive product which acts as an inhibitor of hormone action. In this way, the action of hormone upon a cell could be controlled by the cell itself.
License and Reuse Information
This work is licensed under a Creative Commons Attribution-NonCommercial-Share Alike 4.0 International License.
Recommended Citation
Karlin, Arthur, "The Inactivation of Neurohypophyseal Hormones by the Toad Bladder" (1962). Student Theses and Dissertations. 576.
https://digitalcommons.rockefeller.edu/student_theses_and_dissertations/576
Comments
A thesis presented to the faculty of The Rockefeller University in partial fulfillment of the requirements for the degree of Doctor of Philosophy