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Biomedical subjects

R Walter

Publications and source records attributed to R Walter.

At least 199 records · Page 11Linked to original sources
PubMed1977

An enzymatically stable peptide with activity in the central nervous system: its penetration through the blood-CSF barrier.

Vasopressin, other neurohpophyseal peptides and certain of their fragments can affect central nervous system function. Cyclo(Leu-Gly), formally derived from the C-terminal dipeptide of oxytocin, is also active in memory processes. This molecule, radioactively labeled for this study, was found to be resistant to enzymatic degradation both in vivo and in vitro. Furthermore, after its intravenous application in cat, it easily penetrated into cerebrospinal fluid. This indicates that cyclo(Leu-Gly) can readily pass from blood into the central nervous system to exert it's central pharmacological actions. Thus, labeled cyclo(Leu-Gly) is a valuable model for studying the distribution and localization of peptides which have activity in the central nervous system.

Animals↗
PubMed1977

Combined high oxytocic with negligible antidiuretic and pressor activities in multisubstituted oxytocins.

Oxytocin analogues which combine high oxytocic activities with negligible antidiuretic and pressor activities have been studied. [4-Threonine,7-glycine]oxytocin, [1-(L-2-hydroxy-3-mercaptopropionic acid),4-threonine,7-glycine]oxytocin, and [1-(L-2-hydroxy-3-mercaptopropionic acid)]oxytocin were found to possess the following specific biological activities respectively: rat uterotonic, 270 +/- 10, 337 +/- 23, 1542 +/- 0.4; rat antidiuretic, 0.002 +/- 0.0008, 0.048 +/- 0.005, 40.3 +/- 2.4. The results are analyzed from a conformation-activity viewpoint in a continued attempt to evaluate the scope and limitations of this approach in comparison to structure-activity studies.

Animals↗
PubMed1977

Pharmacological effects of introducing a double bond into a binding site of oxytocin. Analogues with L-3,4-dehydroproline in position 7.

The side chain of the proline residue in position 7 of oxytocin has been proposed as a binding site of the hormone for the uterotonic receptor. This is the first in a series of studies in which the possibility is explored that amino acid residues located at such sites and bearing unsaturated side chains may contribute more strongly to binding than neutral, aliphatic side chains. To test this hypothesis [7-(L-3,4-dehydroproline)]oxytocin, [1-beta-mecaptopropionic acid,7-(L-3,4-dehydroproline)]oxytocin, and [1-L-alpha-hydroxy-beta-mercaptopropionic acid,7-(L-3,4-dehydroproline)]oxytocin were prepared by the solid-phase technique of peptide synthesis. Some of the pharmacological properties of the analogues were determined, and the following specific activities, respectively, were found: rat uterotinic, 1071 +/- 59, 1066 +/- 95, 880 +/- 180; avian vasodepressor, 548 +/- 10, 1008 +/- 42, 1295 +/- 62; rat antidiuretic 5.9 +/- 0.2, 23.3 +/- 1.1, 76.7 +/- 2.3. All analogues possess a lower rat pressor activity than ocytocin. Compared to oxytocin, [7-(L-3,4,-dehydroproline)]oxytocin exhibits a parallel displacement of the cumulative uterotonic log dose vs. response curve toward lower concentration (pD2 = 9.26 vs. 8.63) but elicits the same maximum response. These data would seem to support the hypothesis that the introduction of unsatuation into binding element of a peptide hormone can enhance the affinity of the hormone for some of its receptors and thereby its selectivity.

Animals↗
PubMed1977

Conformation-activity studies of oxytocin. Effects of structural modifications at corner positions of the beta-turns on the uterotonic activity.

Replacement of the aliphatic isoleucine residue in position 3 of oxytocin (the first corner position of the beta-turn in the 20-membered ring of the solution conformation of the hormone) by phenylalanine has been shown to result in analogues with reduced affinity and intrinsic activity when tested by the individual dose-response procedure on the isolated rat uterus. Studies of effects of structural modifications have been extended to include two additional beta-turn corner positions. First, the dose-response behavior of [Leu4]oxytocin and [Phe4]oxytocin, two analogues in which the Glu4 side chain in the second corner position of the beta-turn in the 20-membered ring has been substituted by hydrophobic and bulky groups, was compared with that of oxytocin. Second, the solid-phase synthesis and biological properties of [Phe3,Leu4,Met8]oxytocin and [Phe3,4,Met8]oxytocin are described. The presence of leucine or phenylalanine in position 4 evokes a drastic reduction in both the affinity and intrinsic uterotonic activity of the resulting analogues, with phenylalanine significantly more effective in reducing intrinsic activity than leucine (p less than 0.001).

Animals↗
PubMed1977

Biosynthesis of neurophysin proteins in the dog and their isolation.

Neurophysin (Np) is generally found in close association with vasopressin and oxytocin in the hypothalamo-neurohypophyseal complex. Dog neurophysin I and II have been isolated from fresh and frozen posterior pituitaries. The proteins were characterized on the basis of disc electrophoresis, immunological properties, amino acid composition and partial sequence determination. The amino terminal sequence of dog Np I is Ala-Ala-Leu-Asp-Leu-Asp-Val-Arg-Gln-Cys-Leu-Pro-Cys-Gly-Pro-Gly-Gly-Gln-Gly-while that of dog Np-II is Ala-Met-Ser-Asp-Leu-Glu-Leu. The dog Np I appears to be metabolically less stable than Np II. Isotope experiments with [35S]cystine or 3H-labeled amino acids using a design of "in vitro pulse and in vitro chase" as well as "in vivo pulse and in vivo chase," added further confirmation of the capability of the hypothalamic neurosecretory cells to synthesize concomitantly precursors of Np and vasopressin. The radioactively labeled precursors were converted to Np-like protein and vasopressin, both of which were isolated.

Amino Acid Sequence↗
PubMed1977

Dose-response behavior on the isolated rat uterus of oxytocin analogs with modifications at binding sites.

The dose-response behavior on the in vitro rat uterus of analogs of oxytocin with modification at sites in the molecule which have been predicted to contribute to the binding of the peptide to the smooth muscle receptor have been studied. Dose-response curves of [7-(3,4-dehydroproline)]oxytocin, [7-glycine]oxytocin, [7-alanine]oxytocin, deamino-[7-glycine]oxytocin and [4-threonine,7-glycine]oxytocin were determined and compared with that of oxytocin. The authors found that neither the slope of the curves nor the maximal response obtained for any of the analogs differed significantly from the hormone. The uterotonic potencies of the analogs corresponded to the relative positions along the concentration axis of their dose-response curves and to their affinities as determined by their pD2 values. The authors tentatively concluded that differences in uterotonic potencies of these analogs are in fact the result of differences in their affinity for the uterine receptor. The experimental identification of position 7 of neurohypophyseal peptides as a hormone-receptor binding site corroborates such a proposed role for the side chain of this residue based on earlier conformation-activity considerations.

Animals↗
PubMed1976

Intramolecular 1H nuclear Overhauser effect study of the solution conformation of valinomycin in dimethyl sulfoxide.

Determination of the mechanism of intramolecular nuclear Overhauser effects (NOE) in peptides and depsipeptides is essential to the use of this technique in conformational analysis of these and related biomolecules. Towards this end, 1H NMR double-resonance studies were conducted on valinomycin in (CD3)2SO at 90 MGZ (FT mode) and 250 MGZ (correlation mode). The NOE's are positive at the lower frequency and negative at the higher frequency. Consideration of the theoretical dependence of the NOE on the proton-proton internuclear correlation time and on the resonance frequency indicates that these results are explained by a predominantly dipolar relaxation mechanism. It is demonstrated that exchange modulation of scalar coupling does not contribute significantly to the NOE. A formalism for the NOE's of loosely coupled spin systems is presented which takes into account the effects of high magnetic-field strengths and long correlation times. An approximate analysis of the NOE data assuming a single correlation time for the entire molecule and ignoring cross-relaxation effects was used to evaluate various models that have been proposed for the conformation of valinomycin. The III-1 model of Patel and Tonelli (Patel, D.J., and Tonelli, A.E. (1973), Biochemistry 12, 486) fits the NOE and peptide NHCalphaH coupling constant data and is probably a preferred orientation in dimethyl sulfoxide. These experiments illustrate how intramolecular NOE data provide a valuable auxiliary method to other techniques for delineating the preferred solution conformation of peptides, depsipeptides, and other biomolecules.

Binding Sites↗
PubMed1976

Post-proline cleaving enzyme. Purification of this endopeptidase by affinity chromatography.

The endopeptidase, post-proline cleaving enzyme, has been purified 10,500-fold in an overall yield of 18% from lamb kidney. The enzyme possesses a specific activity of 45 mumol/mg/min as tested with the substrate Z-Gly-Pro-Leu-Gly (Km = 6.0 X 10(-5)), has a molecular weight of 115,000, is comprised of two subunits with a molecular weight of 57,000, and exhibits maximal activity at pH 7.5 to 8.0. With the exception of the -Pro-Pro linkage, the -Pro-X-peptide bond (X equals L- and D-amino acid residues) located internally in the peptide sequence can be hydrolyzed (cleavage occurs faster when X = lipophilic side chain as compared to X = acidic side chain). The appropriate -Pro-X- bonds in zinc-free porcine insulin, oxytocin, arginine vasopressin, angiotensin II, bradykinin-potentiating factor were cleaved. Human gastrin, adrenocorticotropic hormone, denatured guinea pig skin collagen, and ascaris cuticle collagen were not degraded. Dipeptides with the structure Z-Pro-LD-X competitively inhibit post-proline cleaving enzyme.

Animals↗