[5-(N4,N4-Dimethylasparagine),8-lysine]vasopressin: the first 5-position neurohypophyseal hormone analogue to retain to retain significant antidiuretic potency

In the proposed biologically active conformation of vasopressin at the antidiuretic receptor, the side-chain carboxamide group of the 5-position asparaginyl residue has been previously suggested to be the key active element in the hormone for its initiation of the antidiuretic response. [5-(N4,N4-Dimethylasparagine),8-lysine]vasopressin, the analogue in which the hydrogen atoms of the -NH2 portion of the primary carboxamide have been replaced by methyl groups, has been synthesized and found to retain about 3% of the antidiuretic potency of lysine-vasopressin (i.e., 5.5 +/- 0.3 units/mg). This result suggests that the hydrogen atoms of the carboxamide moiety are not essential for antidiuretic activity. In addition, the analogue possesses rat pressor, avian vasodepressor, and rat uterotonic potencies of 2.55 +/- 0.05, 0.39 +/- 0.03, and less than 0.05 units/mg, respectively.

Oxytocin and lysine-vasopressin with N5,N5-dialkylglutamine in the 4 position: effect of introducing sterically hindered groups into the hydrophilic cluster of neurohypophyseal hormones

The synthesis and pharmacological potencies of oxytocin and lysine-vasopressin analogues are reported in which the N5-amide of their glutaminyl residues are dialkylated. These analogues have been studied as an ongoing exploration of the biological effects on the natural hormones of substituting individually one of the amino acid residues, which has a hydrophilic side chain and which are thought to be part of the hydrophilic surface of the hormones. [4-(N5,N5-Dimethylglutamine)]oxytocin (17), [4-(N5,N5-di-n-propylglutamine)]oxytocin (18), and [4-(N5,N5-dimethylglutamine)] lysine-vasopressin (19) were synthesized by clasical solution techniques. Potencies in the in vitro rat uterotonic, avian vasodepressor, rat pressor, and rat antidiuretic assays were determined and are as follows, respectively: for compound 17 3.01 +/- 0.14 units/mg, 4.55 +/- 0.03 units/mg, tachyphylaxis and tachyphylaxis; for compound 18 less than 0.1, less than 0.1, less than 0.05, and less thad 1.88 +/- 0.04 units/mg. The potencies in all cases are significantly less than those of the parent hormone. The results are discussed in terms of the proposed biologically active conformations of the hormones at the uterotonic receptor and at the antidiuretic receptor.

Carboxamidopeptidase: purification and characterization of a neurohypophyseal hormone inactivating peptidase from toad skin

Carboxamidopeptidase, an enzyme which inactivates neurohypophyseal hormones, has been purified 3800-fold in an overall yield of 22% from toad skin, a neurohypophyseal hormone target organ, by (NH4)2SO4 fractionation, DEAE-Sephadex chromatography, and affinity chromatography on immobilized p-aminobenzamidine and concanavalin A-agrose. The purified enzyme is capable of inactivating both [8-arginine]vasopressin (AVP) and oxytocin by hydrolyzing the Arg8-Gly9-NH2 and the Leu8-Gly9-NH2 bonds, respectively, and can hydrolyze the ester substrates, benzoyl-L-arginine ethyl ester (BzArgOEt) and acetyl-L-trypsine ethyl ester, suggesting that the enzyme has both trypsin-like and chymotrypsin-like activities. Carboxamidopeptidase is maximally active at pH 7.5-8.5 for AVP and BzArgOEt and pH 7.0 for oxytocin. Carboxamidopeptidase is inhibited by ovoinhibitor, ovomucoid, Trasylol. lima bean trypsin inhibitor, concanavalin A, antipain, leupeptin, chymostatin, elastatinal, p-nitrophenyl p-guanidinobenzoate, and 4-methylumbelliferyl p-guanidinobenzoate but not by soybean trypsin inhibitor, alpha 1-antitrypsin, hirudin, pepstatin, bestatin, phosphoramidon, or cysteine. The enzyme is also inhibited by the serine protease inhibitor, diisopropyl phosphofluoridate (i-Pr2PF), and by the chloromethyl ketone derivatives of tosyllysine, tosylphenylalanine, and (benzyloxycarbonyl)phenylalanine, as well as by the sulfhydryl group reagent, p-(chloromercuri)benzoate (PCMB). Inhibition by PCMB is reversed by cysteine. The molecular weight determined by gel filtration in the presence of 1 MNaCl is approximately 100 000. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicates that the enzyme is composed of two identical subunits of 48 000 daltons. Each subunit consists of a heavy chain (28 000 daltons) and a light chain (19 000 daltons) joined by a disulfide bond(s). Labeling experiments using [3H]-i-Pr2PF showed that the enzyme active site is located in the heavy chain.

Development of narcotic tolerance and physical dependence: effects of Pro-Leu-Gly-NH2 and cyclo (Leu-Gly)

Administration of Pro-Leu-Gly-NH2 (MIF) and cyclo (Leu-Gly) blocked the development of tolerance to and physical dependence on morphine, induced by the pellet implanation procedure in mice. Inhibition of tolerance development by peptides was evidenced by the presence of an analgesic response (increase in jump threshold) as determined by measuring the jump threshold to an increasing electric current, after a challenge dose of morphine (40 mg/kg). The same dose of morphine did not alter the jump threshold in morphine tolerant mice which were injected with saline prior to pellet implantation. The inhibition of the development of physical dependence on morphine by these peptides was evidenced by the antagonism of the hypothermic response which occurs during abrupt or naloxone-induced withdrawal. The naloxone-induced withdrawal jumping response was unaffected by these peptides. Dose-response experiments indicated that cyclo (leu-Gly) was much more potent than MIF in these tests. These peptides, when given after the development of tolerance and dependence, did not modify either the analgesic response to morphine or the symptoms of abrupt and naloxone-precipitated withdrawal. The inhibition of development of analgesic tolerance and physical dependence was not associated with changes in brain morphine concentration. The data indicate that these peptides do not interfere withe the morphine-morphine receptor complex formation but alter a subsequent step in the genesis of some aspects of tolerance and dependence processes.

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.

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.

Post-proline cleaving enzyme. Synthesis of a new fluorogenic substrate and distribution of the endopeptidase in rat tissues and body fluids of man

Synthesis and application of the first fluorogenic substrate, N-carbobenzoxyglycylprolyl-4-methylcoumarinyl amide (Z-Gly-Pro-MeCouNH) for the determination of the post-proline cleaving enzyme (EC 3.4.21.-) were reported. Maximal activity of the enzyme purified from lamb kidney for the new substrate was observed at pH 7.0. This substrate showed a higher affinity (Km = 0.02 mM) for the enzyme than the proline containing substrates studied previously and allowed the detection of 10-50 ng post-proline cleaving enzyme activity per ml sample after a 1 min incubation period. Distribution of post-proline cleaving enzyme and other proline specific peptidases in rat tissues was studied using Z-Gly-Pro-MeCouNH and other proline-containing substrates. High post-proline cleaving enzyme activity was observed in testis, liver and skeletal muscle. Inhibition experiments indicated that post-proline cleaving enzyme activity was completely inactivated by 0.1 mM diisopropylphosphofluoridate and Z-Gly-Pro-chloromethylketone, as had been found in the case of the enzyme isolated from lamb kidney. Activity in human body fluids was also tested for levels of post-proline cleaving enzyme activity using Z-Gly-Pro-MeCouNH and semen was found to show the highest cleaving activity.

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.

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.

Distribution, survival and biological effects in mice of a behaviorally active, enzymatically stable peptide: pharmacokinetics of cyclo(Leu-Gly) and puromycin-induced amnesia

Cyclo(Leu-Gly), the enzymatically resistant diketopiperazine formally derived from the C-terminal dipeptide sequence of oxytocin, exhibits activity in several behavioral systems. The distribution of cyclo(Leu-14C(U)Gly) in brain, and the time course of the disappearance of this labeled peptide from brain and plasma after subcutaneous injection into mice have been studied. The intact peptide was distributed equally in the five cerebral areas studied, for up to 96 hours after injection. Two exponential components were determined for peptide disappearance rates in plasma and brain; peptide half-lives in plasma up to 10 hr and from 24--96 hr after injection were, respectively, 0.8 and 33 hr; in brain, 1.0 and 42 hr. The peptide was found to accumulate in brain intracellular space to some degree. The time course of distribution of labeled cyclo(Leu-Gly) in subcellular fractions of mouse brain was also examined, and the concentration of peptide in the synaptosomal fraction was significantly correlated with the degree of protection against puromycin-induced amnesia of a maze-learning test. The results obtained not only confirm that cyclo(Leu-Gly) penetrates brain tissue intact and remains intact after peripheral administration in order to exert its behavioral effects, but, moreover, suggest an intriguing dynamic relationship between peptide concentration in the synaptosomal fraction and behavioral activity.

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.

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.

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.