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Biomedical subjects

R Walter

Publications and source records attributed to R Walter.

At least 163 records · Page 9Linked to original sources
PubMed1979

Amide hydrogen exchange rates of peptides in H2O solution by 1H nuclear magnetic resonance transfer of solvent saturation method. Conformations of oxytocin and lysine vasopressin in aqueous solution.

The NH exchange rates in aqueous media of oxytocin and 8-lysine vasopressin (LVP) have been measured by using transfer of solvent saturation method. The data are consistent with a "highly motile" dynamic equilibrium between folded and highly solvated conformations. The highly-motility limit applies to the exchange of NH hydrogens of oxytocin and LVP. Folded structures are more prevalent in oxytocin than in LVP. Partial shielding is indicated for peptide hydrogens of Asn5 and perhaps also Cys6 of oxytocin and for Cys6 of LVP. It is tentatively proposed that the folded conformation of oxytocin in aqueous media may contain a parallel beta-structure in the tocinamide ring consisting of two hydrogen bonds: one between the Tyr2 C = O and Asn5 peptide NH as originally proposed for the preferred conformation of oxytocin in dimethyl sulfoxide (D. W. Urry and R. Walter), and the second between he Cys1 C = O and the Cys6 NH. In LVP the hydrogen bond between the Tyr2 C = O and Asn5 peptide NH appears to be absent. The acylic tripeptide sequences (-Pro-X-Gly-NH2) of both hormones appear to be predominantly solvated. The second-order rate constants for acid catalyzed exchange of the primary amide hydrogens of Gln4, Asn5, and Gly9 of oxytocin are consistently greater for the trans NH than for the corresponding cis NH. This observation can be rationalized in terms of mechanisms involving protonation of either the amide oxygen, or the amide nitrogen, but with limited rotation about the C - N bond.

Lypressin↗
PubMed1979

Active-site studies of neurohypophyseal hormones: synthesis and pharmacological properties of [5-(N4,N4-dimethylasparagine)]oxytocin.

Synthesis and biological properties of [5-(N4,N4-dimethylasparagine)]oxytocin are reported. In this analogue, the hydrogens of the primary carboxamide moiety in the side chain of the asparagine residue in position 5 of the posterior pituitary hormone oxytocin have been replaced by two methyl groups. The protected nonapeptide intermediate was prepared by a stepwise procedure using solution techniques. The analogue possesses 4.60 +/- 0.03 units/mg (mean +/- SEM) uterotonic activity on the isolated rat uterine horn and 9.14 +/- 0.03 units/mg of avian vasodepressor activity. Moreover, it displays an identical intrinsic activity in the in vitro rat uterotonic assay as oxytocin, when tested in the presence of either 0.5 mM Ca2+ (standard assay conditions) or at reduced levels of Ca2+ (0.3, 0.15, and 0.05 mM). This result is significant in view of the proposed biologically active model of oxytocin, in which the side chain of the 5 position residue was assigned to contain an "active element" responsible for the intrinsic activity of the hormone when bound to the uterine receptor.

Animals↗
PubMed1979

Prolyl-leucyl-glycinamide, cyclo(leucylglycine), and derivatives block development of physical dependence on morphine in mice.

Pro-Leu-Gly-NH2 (MIF) and several structural analogues, all injected in 50-microgram doses daily in mice receiving morphine chronically, were found to prevent development of physical dependence as measured by changes in body temperature associated with naloxone-induced withdrawal. Dose-response studies, using again a protocol of daily injections of peptide at 50, 5, 0.5, 0.05, 0.005 microgram per mouse revealed MIF and cyclo(Leu-Gly) to be the most potent peptides and to be effective in blocking physical dependence to morphine at a dose as low as 0.5 and 0.05 microgram per mouse, respectively. The benzyloxycarbonyl derivative of MIF, Pro-Leu, and Pro- -Leu exhibited significant activities down to a dose of 5 microgram of peptide per mouse.

Animals↗
PubMed1979

Blockage of narcotic-induced dopamine receptor supersensitivity by cyclo(Leu-Gly).

We have previously reported that the administration of cyclo(Leu-Gly) to mice prior to morphinization blocked the development of tolerance to the analgesic effects of morphine as well as the development of some signs of physical dependence. In the present series of experiments, the effect of the same peptide treatment on changes in dopamine receptor sensitivity induced by chronic morphine treatment were determined. Changes in dopamine receptor sensitivity were determined by measuring (i) the effect of the dopamine agonist apomorphine on locomotor activity and (ii) the hypothermic response to another dopamine agonist, piribedil. Mice that had received the chronic morphine treatment were found to require significantly less apomorphine to produce an increase in locomotor activity, and they exhibited a significantly greater hypothermic response to piribedil than did morphine-naive mice. The injection of 0.2 mumol of cyclo(Leu-Gly) per mouse 2 hr prio to morphine treatment prevented this increased response to both dopamine agonists. Administration of the peptide after the tolerance and dependence had developed did not alter morphine tolerant and dependent states states or the enhanced response to apomorphine or piribedil. It is concluded that dopamine receptor supersensitivity may be involved in the development of narcotic tolerance and physical dependence.

Animals↗
PubMed1979

Poly-N-acrylylpyrrolidine. A new resin in peptide chemistry.

Entirely beaded poly-N-acrylylpyrrolidine-co-bisacrylyl-1,2-diaminoethane-co-N-acrylyl-1,6-diaminohexane.HCl(PAP), a new resin on which to perform peptide chemistry, has been prepared by reverse phase suspension polymerization in quantitative yield. In addition to being a superior support to polystyrene, albeit readily adaptable to current techniques of peptide synthesis, its versatility has been furthur extended by the introduction and use of new peptide-to-polymer linking groups, which allow the use of the bidirectional approach to peptide chemistry. One such linkage, which connects the side chain of cysteine to PAP via an acid resistant S-carbamoyl bond, was used in a bidirectional synthesis of deamino-oxytocin. PAP solvates and swells in solvents with wide-ranging polarities, including aqueous media. Thus, peptide coupling reactions were performed in organic media of high and of low polarity as well as in aqueous solution.

Amino Acid Sequence↗
PubMed1979

Effects of D and L amino acid residues in linear peptides on carbon-13 nuclear magnetic resonance parameters.

The 13C spectra of the linear tripeptidyl diastereoisomers, Gly-Gly-Leu, Gly-Gly-D-Leu, Leu-Gly-Gly, D-Leu-Gly-Gly, Ala3, Ala-Ala-D-Ala, Ala-D-Ala-Ala, Val3, and Val-Val-D-Val are very similar or even identical at pH meter readings of 1.0, 7.0 and 12.0 in D2O. The spectra of Pro-Leu-Gly-NH2 and Pro-D-Leu-Gly-NH2 likewise show only minor differences in 13C chemical shifts (less than 0.4 p.p.m.) under similar conditions. This contrasts significantly with previous findings comparing 13C chemical shifts of cyclo(Pro-Leu) and cyclo(Pro-D-Leu) where major differences in chemical shifts were observed for both residues due to differences in conformational constraints present in these cyclic proline-containing peptides. The least-squares fit of spin-lattice relaxation times (T1) for Pro-Leu-Gly-NH2 and Pro-D-Leu-Gly-NH2 show that it is not possible to fit all the T1 values to a unique and rigid structure whether folded or extended. The glycyl residue undergoes enhanced motion when compared with the prolyl and leucyl residues. Internal motion must be postulated within the proline ring and for the CH3 groups of leucine.

Amino Acid Sequence↗
PubMed1979

Bovine neurophysin lipid complex. Their isolation, characterization and reaggregation.

A lipid-containing neurophysin fraction was isolated and purified from bovine posterior pituitary glands by acid extraction and affinity chromatography on a heparin-Sepharose 4B column. This lipid-rich fraction was found to be composed of noncovalent aggregates of neurophysin proteins and phospholipids such as phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine and sphingomyelin. The lipid-containing neuophysin was delipidated by treatment with choloform-methanol. The resultant apoproteins were characterized as bovine neuroions were developed for the reaggregation of purified bovine neurophysin-I and -II with lipids extracted from bovine posterior pituitary and hypothalamus and with synthetic lecithin. The resultant neurophysin lipid complexes have been shown to band upon isopycnic centrifugation at densities different from those of the respective purified bovine neurophysins.

Animals↗
PubMed1978

Conformational studies on [Pro3, Gly4]-oxytocin in dimethyl sulfoxide by 1H nuclear magnetic resonance spectroscopy: evidence for a type II beta turn in the cyclic moiety.

A model for oxytocin has been previously proposed in which residues 3 and 4 occupy the corner positions in a beta turn (Urry, D. W., & Walter, R (1971) Proc. Natl. Acad. Sci. U.S.A. 68, 956). The analogue [Pro(3),Gly(4)]-oxytocin (PGO) was used in proton magnetic resonance (1H NMR) studies designed to probe the contribution of these corner positions in forming a beta turn. Comparison of various 1H NMR parameters obtained at 220 MHz for backbone amide protons of PGO with those for the corresponding protons of oxytocin suggests that, to a first approximation, these two peptides may have similar backbone conformations in )CD3)2SO. Theoretically, the L-Pro lead toGly sequence in positions 3 and 4 of PGO would allow the formation of either a type I or type II beta turn. The two coupling constants between vicinal amide and C alpha protons for Gly(4) of PGO in (CD3)2SO are compatible with a type II beta turn in which 04, the dihedral angle about the bond between the backbone C alpha and N' atoms of Gly4, is appromximately +92 degrees, but not with a type I beta turn. A survey of peptides studied in other laboratories by X-ray and/or 1H NMR with reported type II beta turns with L-Pro lead toGly or Gly lead to Gly sequences in the corner positions revealed a close correlation between chemical shifts and vicinal coupling constants for the glycl residue in the second corner position. It is suggested that this criterion can form an additional basis for the characterization of beta turns. More studies are needed to determine the particular type of beta turn manifest in the cyclic moiety of oxytocin per se, although a reasonable working hypothesis is that oxytocin, similar to PGO, has a type II beta turn.

Dimethyl Sulfoxide↗
PubMed1978

Postproline cleaving enzyme: kinetic studies of size and stereospecificity of its active site.

Postproline cleaving enzyme [EC 3.4.21.-] has recently been purified from lamb kidney and tentatively identified as a serine endopeptidase with a high specificity for proline-containing peptides. The interaction of postproline cleaving enzyme with peptide substrates and competitive inhibitors has been studied in an effort to explore the size and stereospecificity of the active site of the protease. The substrates and inhibitors included proline-containing peptide amides, p-nitrophenyl esters, and free acids with increasing numbers of amino acid residues and residues of L and D configuration. Oligopeptides of alanine, which can also be recognized by the protease, were also tested as substrates. This series included Ala3, Ala-D-Ala-Ala, Ala-Ala-D-Ala,Z-(Ala)3, Ala4 through Ala6. The contribution of each of the three amino acid residues flanking the primary specificity site (S1) of postproline enzyme to such kinetic parameters as Km, Kcat, and Kcat/Km in the case of substrates and Ki with inhibitors was determined. The results suggest that postproline cleaving enzyme has an extended substrate binding region in addition to the primary specificity site, S1. It seems to be comprised of three sites located at the amino-terminal site (S1, S2, and S3) and two sites at the carboxyl site from the catalytic point (S1', S2'). High stereospecificity was observed for subsites S1, S2, and S1'.

Animals↗
PubMed1978

Complete amino acid sequence of bovine neurophysin-I. A major secretory product of the posterior pituitary.

Bovine neurophysin-I (bNP-I) is the first neurophysin protein which contains histidine and possesses an acidic COOH-terminal segment for which the complete amino acid sequence is presented: NH2-Ala-Val-Leu-Asp-Leu-Asp-Val-Arg-Thr-Cys-Leu-Pro-Cys-Gly-Pro-Gly-Gly-Lys-Gly-Arg-Cys-Phe-Gly-Pro-Ser-Ile-Cys-Cys-Gly-Asp-Glu-Leu-Gly-Cys-Phe-Val-Gly-Thr-Ala-Glu-Ala-Leu-Arg- Cys-Gln-Glu-Glu-Asn-Tyr-Leu-Pro-Ser-Pro-Cys-Gln-SerGly-Gln-Lys-Pro-Cys-Gly-Ser- Gly-Gly-Arg-Cys-Ala-Ala-Ala-Gly-Ile-Cys-Cys-Ser-Pro-Asp-Gly-Cys-His-Glu-Asp-Pro-Ala-Cys-Asp-Pro-Glu-Ala-Ala-Phe-Ser-Leu-COOH. Determination of the structure was greatly facilitated by new procedures used for the isolation of bNP-I and of its tryptic peptide fragments. bNP-I isolated from freshly frozen bovine posterior pituitaries is composed of 93 residues, but some preparations contain neurophysin protein with NH2- and COOH-terminal truncated sequences. bNP-I differs from bovine neurophysin-II, the second major neurophysin of cow, in 20 residue positions, and several of the differences cannot be accounted for by single nucleotide replacements in the genes coding for these two neurophysin proteins. The results reported in this study support our earlier hypothesis that neurophysin-gene duplication preceded species divergence.

Amino Acid Sequence↗