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Biomedical subjects

R Walter

Publications and source records attributed to R Walter.

At least 289 records · Page 16Linked to original sources
PubMed1971

Leucylglycinamide released from oxytocin by human uterine enzyme.

Uteri of pregnant and nonpregnant women contain enzymic activities which inactivate oxytocin. A potent enzyme, which has been partially purified from uterine homogenates, cleaves the prolyl-leucyl peptide bond of oxytocin. This findinig associates for the first time the release of the dipeptide leucylglycinamide with the degradation of neurohypophyseal hormones.

Buffers↗
PubMed1971

Proposed conformation of oxytocin in solution.

A conformation of the neurohypophyseal hormone oxytocin in solution is proposed. The structure possesses, in addition to the beta-turn comprised of the sequence -L-tyrosyl-L-isoleucyl-L-glutaminyl-L-asparaginyl- in the ring component of the hormonal molecule, a second beta-turn involving the C-terminal oxytocin sequence, -L-cysteinyl-L-prolyl-L-leucylglycinamide. The resulting oxytocin structure places the bulky side chains of the leucine and isoleucine residues, as well as the cyclic moiety of the proline residue, at corners of the two beta-turns. A critical role is played by the asparagine residue: its peptide N-H participates in the formation of the hydrogen-bonded cyclic structure of the beta-turn in the ring component of oxytocin and its peptide C=O can be hydrogen-bonded to the N-H of tyrosine, while its side chain C=O stabilizes the second beta-turn by forming a hydrogen bond with the N-H of the leucine residue, which is part of the end peptide of the second beta-turn. This conformational assignment of oxytocin is consistent with hydrogen-deuterium exchange studies, with plots of temperature dependence of peptide proton chemical shifts, and with the coupling constants for the NH-CH dihedral angles.

Amino Acid Sequence↗
PubMed1971

Relation of the conformation of oxytocin to the biology of neurohypophyseal hormones.

The conformation of oxytocin is related to the evolution and to some of the biological activities of neurophypophyseal hormonal peptides. On the basis of the three-dimensional structure, positions 3, 4, 7, and 8 are the only loci at which naturally occurring neurohypophyseal peptides may be expected to differ. The side chains of these amino-acid residues are the primary determinants of the differential specificity in interactions between neurohypophyseal hormones and their receptors. THERE ARE THREE GENERAL GROUPS OF STRUCTURAL MODIFICATIONS OF NEUROHYPOPHYSEAL HORMONES WHICH CAN BE CORRELATED WITH SPECIFIC CHANGES IN BIOLOGICAL ACTIVITY: (a) those affecting the stabilization of the backbone of the peptide, which would extensively perturb the spatial relationships among all the constituent amino acids and hence, affect both affinity and intrinsic activities uniformly; (b) those which, while retaining the stability of the backbone conformation, alter the steric environment and charge distribution of limited surface areas, and thereby can affect affinity and intrinsic activity differentially; and (c) those changing the steric and electronic requirements of moieties comprising the active surface of the neurohypophyseal peptide, without perturbing the peptide backbone of the hormone molecule and, hence, affecting intrinsic activity without altering affinity.

Amino Acid Sequence↗
PubMed1971

Regulation of formation and proposed structure of the factor inhibiting the release of melanocyte-stimulating hormone.

Microsomal preparations from the stalk median eminence of female rats are shown to contain an enzymic activity that is responsible for the formation of MSH-release-inhibiting factor (MSH-R-IF). The amount of this activity remains constant throughout the estrous cycle. The corresponding mitochondrial preparations from the stalk median eminence contain another enzymic principle, estrous cycle-dependent, which competes with the enzyme present in the microsomal preparation for the same "substrate", and can thereby prevent the formation of MSH-R-IF. Several neurohypophyseal hormones, analogs, and peptide intermediates have been tested for their intrinsic MSH-R-IF activity and for their ability to be transformed into MSH-R-IF by incubation with microsomal preparations of stalk median eminence from male rats; it is concluded that the enzyme responsible for the formation of MSH-R-IF is an exopeptidase and that the release-inhibiting factor itself is a tripeptide. Oxytocin is converted by the incubation to (L)-prolyl-(L)-leucylglycinamide; nanogram amounts of this tripeptide inhibit the release of MSH from the pituitary both in vivo and in vitro.

Animals↗
PubMed1971

Neurohypophyseal hormone-responsive adenylate cyclase from mammalian kidney.

The investigation was undertaken to evaluate the direct stimulatory effects of neurohypophyseal hormones upon adenylate cyclase activity in a cell-free, particulate fraction derived from the kidney medulla of various mammalian species. The relative affinity of neurohypophyseal hormones for the receptor component of the adenylate cyclase system (as defined by the concentration of hormone required for half-maximal stimulation) had the order [8-arginine]-vasopressin > [8-lysine]-vasopressin >> oxytocin (AVP > LVP >> OT) for rat, mouse, rabbit, and ox; in the pig, the order was LVP > AVP >> OT. The relative affinities of the three hormones in rat and pig cyclase systems were found to correspond with the relative antidiuretic potencies of these hormones in the intact rat and pig. These findings show that the renal receptor for neurohypophyseal hormones in a particular species exhibits the highest affinity for the specific antidiuretic hormone that occurs naturally in that species. Some of the molecular requirements for the stimulation of rabbit adenylate cyclase were defined by studies of several neurohypophyseal analogs possessing structural changes in positions 1, 2, 3, 4, 5, 8, and 9. This investigation introduces the particulate preparation of renal medullary adenylate cyclase as a tool for the analysis of neurohypophyseal hormone-receptor interactions and indicates that this preparation can be adapted to serve as an in vitro bioassay system for antidiuretic hormonal activity.

Adenylyl Cyclases↗
PubMed1971

Correlation between pinocytosis and hydroosmosis induced by neurohypophyseal hormones and mediated by adenosine 3',5'-cyclic monophosphate.

The isolated urinary bladder of the toad responds to neurohypophyseal hormone with a net increase of water transport from the mucosal to the serosal solution in the presence of an osmotic gradient. This response is mediated intracellularly by cyclic 3',5'-adenosine monophosphate (AMP). The present study demonstrates that hydroosmotically active substances such as oxytocin, dibutyryl cyclic 3',5'-AMP, and theophylline, but not hydroosmotically inactive substances, induce the uptake of horseradish peroxidase from the mucosal solution. Peroxidase taken up by the mucosal cells is demonstrable in small tubules and vesicles, and eventually accumulates in lysosomes. The uptake of peroxidase from the serosal solution into similar bodies in the mucosal cells is not hormone-dependent. It is also shown that peroxidase does not penetrate the tight junction from either the mucosal or serosal solution. These results extend previous findings which implicated the apical membrane of the mucosal epithelium as the site affected by neurohypophyseal hormones. A mechanism based on secretory phenomena is proposed as a framework for future investigations of apical membrane permeability changes and pinocytosis.

Acid Phosphatase↗
PubMed1970

[8-Arginine]-vasopressinoic acid: an inhibitor of rabbit kidney adenyl cyclase.

Neurohypophyseal hormnones and several synthetic analogs stimulate adenyl cyclase prepared from rabbit kidney medullary tissue. [8-Arginine]-vasopressinoic acid inhibits the stimulation of medullary adenyl cyclase by neurohypophyseal peptides but does not influence the action of parathyroid hormone on adenyl cyclase from kidiney cortex.

Adenylyl Cyclase Inhibitors↗