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K Neubert

Publications and source records attributed to K Neubert.

At least 55 records · Page 3Linked to original sources
PubMed1991

Are diprotin A (Ile-Pro-Ile) and diprotin B (Val-Pro-Leu) inhibitors or substrates of dipeptidyl peptidase IV?

Dipeptidyl peptidase IV preferably hydrolyzes peptides and proteins with a penultimate proline residue. Umezawa and co-workers (Umezawa et al. (1984) J. Antibiotics 37, 422-425) reported that diprotin A (Ile-Pro-Ile) and diprotin B (Val-Pro-Leu) are inhibitors for dipeptidyl peptidase IV. We could show that both compounds as well as other tripeptides with a penultimate proline residue are substrates for dipeptidyl peptidase IV. An apparent competitive inhibition by those compounds is a kinetic artifact due to the substrate-like structure of such tripeptides.

Amino Acid Sequence↗
PubMed1991

Cyclization studies with tetra- and pentapeptide sequences corresponding to beta-casomorphins.

The tetrapeptide Boc-D-Orn-Phe-D-Pro-Gly-OH and the pentapeptide sequence Boc-Tyr(tBu)-D-Orn-Phe-D-Pro-Gly-OH were used to study the influence of different coupling reagents on the yield and purity of these model peptides. The simple structure prevented racemization and cyclodimerization and facilitated the ring formation. The most favorable effects on yield and purity were obtained in both reactions using diphenyl-phosphoryl azide (DPPA) and norborn-5-ene-2,3-dicarboximidodiphenylphosphate (NDPP), while the cyclizations with the powerful activating reagents benzotriazol-1-yl-oxy-tris(dimethylamino)-phosphonium hexafluorophosphate (BOP) and 2-(1-H-benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate (HBTU) with the exception of the cyclopentapeptide reaction with HBTU/4-dimethylaminopyridine gave unsatisfactory results.

Amino Acid Sequence↗
PubMed1991

Dipeptidyl peptidase IV in the immune system. Effects of specific enzyme inhibitors on activity of dipeptidyl peptidase IV and proliferation of human lymphocytes.

Dipeptidyl peptidase IV (DP IV) is a membrane peptidase playing a significant role in the process of activation and proliferation of human thymus-derived lymphocytes. This conclusion is drawn from (1) the induction of this enzyme on mitogen-activated T lymphocytes (cf. Schön, E. & Ansorge, S. (1990) Biol. Chem. Hoppe-Seyler 371, 699-705) and (2) the impairment of different functions of activated T cells in the presence of specific inhibitors and antibodies against DP IV (Schön, E. & al. (1987) Eur. J. Immunol 17, 1821-1826). This paper is aimed at testing new active site-specific peptide inhibitors for their efficiency as inhibitors of lymphocyte DP IV and DNA synthesis of mitogen-stimulated lymphocytes. These inhibitors comprise (i) diacylhydroxylamine derivatives of Xaa-Pro or Xaa-Ala peptides, (ii) different oligopeptides with N-terminal Xaa-Pro-sequences, and (iii) amino-acid amides of the pyrrolidide and the thiazolidide type. The thiazolidides of epsilon-(4-nitrobenzyloxycarbonyl)-L-lysine and of L-isoleucine as well as Ala-Pro-nitrobenzoylhydroxylamine are the most effective inhibitors in both test systems, yielding half-maximal inhibitory concentrations in the micromolar range. Cell viability was not impaired in this effective concentration range. Other inhibitors of DP IV are one to two orders of magnitude less efficient in the suppression of lymphocyte proliferation.

Binding Sites↗
PubMed1991

Extended investigation of the substrate specificity of dipeptidyl peptidase IV from pig kidney.

The substrate specificity of dipeptidyl peptidase IV (dipeptidyl peptide hydrolase, EC 3.4.14.5) from pig kidney was investigated, using a series of substrates, in which the amino-acid residue in position P1, a structural derivative of proline, was altered with respect to ring size and substituents. It was demonstrated that dipeptidyl peptidase IV hydrolyses substrates of the type Ala-X-pNA, where X is proline (Pro), (R)-thiazolidine-4-carboxylic acid (Thz), (S)-pipecolic acid (Pip), (S)-oxazolidine-4-carboxylic acid (Oxa), or (S)-azetidine-2-carboxylic acid (Aze). The ring size and ring structure of the residue in the P1 position influence the rate of enzyme-catalysed hydrolysis of the substrate. The highest kcat value (814 s-1) was found for Ala-Aze-pNA. In contrast, the kcat value for Ala-Pro-pNA is nearly 55 s-1. With all substrates of this series, the rate-limiting step of the hydrolysis by dipeptidyl peptidase IV is the deacylation reaction. Compounds of substrate-like structure, in which the P2 residue has an R-configuration, are not hydrolysed by dipeptidyl peptidase IV.

Animals↗
PubMed1991

Structure-activity studies of novel casomorphin analogues: binding profiles towards mu 1-, mu 2- and delta -opioid receptors.

The beta -casomorphin-5 sequence was systematically modified by substitution of the naturally occurring amino acids. The derivatives are compared on the basis of their affinities towards mu 1-, mu 2 and delta -opioid binding sites estimated by means of binding studies with [3H]dihydromorphine and [3H]D-Ala2-Leu5-enkephalin as labels and computer curve fitting. A C-terminal amide group which is known to increase mu-site affinity of beta -CM-4 and beta -CM-5 mainly enhances the mu 2-site affinity. Furthermore, the Pro4-amide structure, which seems to be responsible for the affinity enhancement can be substituted by the pyrrolidide ring structure. Modifications in position 2, 3 and 4 can lead to an increase in mu 1-, mu 2- or delta -site affinity and/or selectivity. The specificity of these effects might be dependent on the respective changes in the charge or hydrophobicity due to the introduction of other amino acids. The results suggest firstly that the alternating proline residues in the beta -CM-5 molecule are not absolutely necessary for its mu-site affinities, and secondly that both opioid receptor subtype affinity and selectivity may be modified by changing charge and/or hydrophobicity in the middle part of the beta -casomorphin molecule.

Amino Acid Sequence↗
PubMed1990

[3H]naloxone as an opioid receptor label: analysis of binding site heterogeneity and use for determination of opioid affinities of casomorphin analogues.

The nonselective antagonist [3H]naloxone was used to identify opioid receptors in rat brain membranes. The multiple naloxone binding sites were related to different opioid receptors by means of selective opioid ligands as well as various beta-casomorphin analogues. Analysis of binding site heterogeneity was performed using several computer curve fitting methods. The results indicate that structurally modified casomorphin peptides are able to discriminate between mu 1- and mu 2-binding sites. The affinities to the mu-sites obtained with [3H]naloxone as label are in a good agreement with those from experiments with the mu-selective radioligand [3H]DAGO. The mu 1-site affinities of these casomorphin derivatives are well correlated with their antinociceptive potencies. This finding suggests the mediation of the analgesic activity via the high-affinity mu 1-subtype.

Affinity Labels↗
PubMed1989

Dipeptidyl peptidase IV in human T lymphocytes. Impaired induction of interleukin 2 and gamma interferon due to specific inhibition of dipeptidyl peptidase IV.

Specific inhibitors of the membrane-bound dipeptidyl peptidase IV (DP IV) and polyclonal antibodies against this enzyme were used to investigate the relationships between DP IV activity and the production and action of T cell-derived lymphokines. Production of interleukin 2 (IL-2) and gamma interferon by mitogen plus phorbol ester-stimulated mononuclear cells from human blood was found to be reduced in the presence of N-Ala-Pro-O-(nitrobenzoyl-)-hydroxylamine, epsilon-(4'-nitro) benzoxycarbonyl-Lys-Pro, and anti-(DP IV) immunoglobulin in a dose-dependent manner. Moreover, the proliferative response of mitogen-stimulated mononuclear cells to IL-2 is impaired in the presence of DP IV inhibitors. Therefore it is suggested that the membrane peptidase DP IV is involved in the induction and activation of cytokines controlling lymphocyte proliferation.

Cells, Cultured↗
PubMed1989

[Application of dipeptidylpeptidase IV in formation of the peptide bond].

According to the increasing importance of enzyme catalysed peptide synthesis the capability of the protease dipeptidyl peptidase IV is shown to form the peptide bond. To our best knowledge, it's the first time that has been used successfully proline as one of the amino acids. The formation of the peptide bond is kinetically controlled. Free amino acids have been used as nucleophiles. The reaction media contain 50 vol.-% glycerol. A first approach to a kinetic treatment is shown.

Amino Acid Sequence↗
PubMed1988

Mechanism of proline-specific proteinases: (I) Substrate specificity of dipeptidyl peptidase IV from pig kidney and proline-specific endopeptidase from Flavobacterium meningosepticum.

The substrate specificity of dipeptidyl peptidase IV (dipeptidyl peptide hydrolase, EC 3.4.14.5) from pig kidney and proline-specific endopeptidase from Flavobacterium meningosepticum, was investigated with a series of N-terminal unprotected (dipeptidyl peptidases IV) and succinylated dipeptidyl-p-nitroanilides (proline-specific endopeptidase). Both enzymes are specific for the S configuration of the amino-acid residue in P1 and P2 position if the penultimate residue is proline. In the case of alanine substrates (Ala in P1, dipeptidyl peptidase IV hydrolyzes such compounds where the configuration of the P2 residue is R. The penultimate residue with dipeptidyl peptidase IV can be, beside proline and alanine, dehydroproline, hydroxyproline and pipecolic acid. Proline substrates (Pro in P1) with an R configuration in P2 are inhibitors of the hydrolysis of proline substrates with an S,S configuration in an uncompetitive (dipeptidyl peptide IV) or mixed inhibition type (proline-specific endopeptidase). Derivatives of Gly-Pro-pNA where the N-terminal amino group is methylated are hydrolyzed by dipeptidyl peptidase IV.

Amino Acid Sequence↗
PubMed1988

Conformational analysis of morphiceptin by NMR spectroscopy.

Three exorphins, beta-casomorphin-5, morphiceptin and its D-Pro4 analog, were studied in DMSO by means of 1H and 13C NMR spectroscopy, with the aim of detecting conformational features of potential biological significance for the mu opioid activity since the presence of two Pro residues restricts the accessible conformational space more than in all other peptides. It is found that the conformational mixtures present in solution contain relevant fractions of folded conformers, a feature that assures the observation of four different Tyr OH signals in the 500 MHz spectrum of morphiceptin. The conformer distribution of (very active) (D-Pro4)-morphiceptin is different from those of its (less active) congeners.

Endorphins↗
PubMed1988

[Detection of dipeptidyl peptidase IV in follicular fluid--initial report].

Aspirates of ovarian follicles were obtained from patients subjected to gynaecologic surgeries. This is the first report of dipeptidyl-peptidase IV (DP IV) activity in human follicular fluid. This enzyme specifically cleaves regulatory important oligo- and polypeptides. Only from peptides with proline or alanine in position P1 of the N-terminal sequence a dipeptide is split off. DP IV activity was measured with glycyl-L-proline p-Nitroanilide as substrate. Levels in a range of 209.8 +/- 57.4 nmol l-1 s-1 were achieved.

Dipeptidyl Peptidase 4↗
PubMed1988

Circulatory activity of dopamine-dipeptide compounds.

Three newly synthesized dopamine-dipeptide compounds (Gly-Pro-dopamide, Lys-Pro-dopamide, Z-Lys-Pro-dopamide) which should be cleft in vivo by the enzyme dipeptidyl peptidase IV (EC 3.4.14.5) were investigated as to their protective activity against hemorrhagic shock in rats. All three compounds increased significantly the survival times of animals, subjected to hemorrhage, in nearly the same manner as dopamine did. They also relaxed the blood vessels of isolated perfused rat kidneys pretreated with phenoxybenzamine. This activity demonstrates a vasodilation via dopaminergic receptors. Regarding the blood pressure increasing activity, mediated by excitation of alpha-receptors, Gly-Pro-dopamide was less potent than dopamine but affected blood pressure about four times longer than dopamine did. Lys-Pro-dopamide and Z-Lys-Pro-dopamide were nearly equieffective to dopamine.

Animals↗
PubMed1988

Effects of beta-casomorphin in isolated heart preparations.

beta-Casomorphin-5, a novel opioid peptide Tyr-Pro-Phe-Pro-Gly, was tested in isolated heart preparations of guinea pigs in comparison with other morphine related peptides and cardioactive drugs. The substance induced a dose-dependent change in the cardiac contraction force, showing a positive inotropic effect in low concentrations (10(-9) - 10(-7) mol/l) but a cardiodepressive action at higher doses (10(-7) - 10(-5) mol/l). Similarly, potentiation phenomena due to varied pacing rates of right-ventricular strips were enhanced at 10(-8) mol/l and lowered at 10(-6) mol/l beta-casomorphin-5. The coronary flow continuously increased. The observed changes of heart action were not mediated by opioid receptors: specifically acting opioid peptides were without influence and naloxone had no inhibitory effect. Peptides with similar sequences may exert a regulatory role in cardiac function, possibly mediated by an influence on the cellular calcium fluxes. The results may prove to be useful for the detection and estimation of more stable and cardioactive peptides.

Animals↗
PubMed1987

The role of dipeptidyl peptidase IV in human T lymphocyte activation. Inhibitors and antibodies against dipeptidyl peptidase IV suppress lymphocyte proliferation and immunoglobulin synthesis in vitro.

Dipeptidyl peptidase IV (DP IV), an ectoenzyme in the cell membrane of T lymphocytes, is an important constituent in the process of lymphocyte activation. This conclusion is drawn from the following observations: (a) Proliferation of peripheral blood lymphocytes induced by mitogenic lectins (phytohemagglutinin, concanavalin A, pokeweed mitogen) is suppressed in the presence of DP IV inhibitors. This effect is specific and applies to an irreversible suicide inhibitor as well as to a competitive one in a dose-dependent fashion. (b) Inhibition of DNA synthesis was also induced by a polyclonal anti-DP IV immunoglobulin. (c) As a consequence of impaired T cell function the production of immunoglobulins by pokeweed mitogen-stimulated lymphocytes is also markedly reduced in the presence of DP IV inhibitors.

Antibody Formation↗
PubMed1987

Role of dipeptidyl peptidase IV in uptake of peptide nitrogen from beta-casomorphin in rabbit renal BBMV.

We examined the handling of radiolabeled beta-casomorphin, Tyr-Pro-[3H]Phe-Pro-Gly, by rabbit renal brush-border membrane vesicles (BBMV). The uptake of radiolabel into the vesicles was Na+-independent, but an inward-directed H+ gradient stimulated the uptake. The H+ gradient-dependent uptake was further accelerated by an interior-negative membrane potential, but inhibited in the presence of a protonophore. Treatment of the membrane vesicles with diisopropylfluorophosphate (DFP) greatly reduced the uptake of the radiolabel. Control as well as DFP-treated vesicles exhibited H+ gradient-dependent Gly-Sar uptake. Unlabeled beta-casomorphin inhibited Gly-Sar uptake in control vesicles, but the inhibition was significantly reduced in DFP-treated vesicles. DFP inhibited the activity of dipeptidyl peptidase IV in these vesicles and there was a direct correlation between the activity of the enzyme and the capacity of beta-casomorphin to inhibit Gly-Sar uptake. Many di- and tripeptides reduced the uptake of Gly-Sar and the uptake of radiolabel from beta-[3H]casomorphin to a similar extent. We conclude that beta-casomorphin is hydrolyzed by dipeptidyl peptidase IV and the products are transported into the vesicles by the H+ gradient-driven peptide transport system. This conclusion is supported by the results from the analysis of the incubation medium by high-performance liquid chromatography that showed rapid hydrolysis of the pentapeptide by brush-border membranes to di- and tripeptides.

Animals↗
PubMed1987

Stepwise degradation of the hexapeptide Met-Ala-Ser-Pro-Phe-Ala by dipeptidyl peptidase IV.

Dipeptidyl peptidase IV (dipeptidyl-peptide hydrolase, EC 3.4.14.-) purified from pig kidney was proved to split off the N-terminal dipeptide Met1-Ala2 and, subsequently the dipeptide Ser3-Pro4 from the synthetic model peptide Met-Ala-Ser-Pro-Phe-Ala representing the N-terminal part of a signal sequence of leucocyte interferon. The kinetic parameters for the release of Met1-Ala2 (Km 3.2.10(-5) mol.l-1 and Ser3-Pro4 (Km 1.65.10(-4) mol.l-1, kcat57.9 s-1) were determined. The dipeptides Ser-Pro and Phe-Ala were found to be competitive inhibitors of the hydrolysis of Gly-Pro-NHNp by dipeptidyl peptidase IV.

Animals↗
PubMed1986

Contamination of highly purified human serum cholinesterase by dipeptidyl peptidase IV causing hydrolysis of substance P.

The purification and kinetic characterization of cholinesterase from blood plasma (pseudocholinesterase; butyrylcholinesterase: EC 3.1.1.8) is described. The hydrolysis of the artificial peptide substrate Lys-Pro-p-nitroanilide served as a model of the second step in degradation of substance P by dipeptidyl peptidase IV. The substrate is hydrolyzed by a gel-electrophoretic homogeneous cholinesterase preparation with a reaction rate of 5.8 mumol/min X mg and a KM value of 0.12 mmol/l. The proteolytic reaction could not be affected with typical cholinesterase inhibitors NaF and dibucain. On the other hand Lys (pNO2-Z)-Pro and a specific suicide substrate (diacylhydroxylamine derivative) inhibit the activity in a manner analogous to dipeptidyl peptidase IV. Though these active site-directed inhibitors also influenced the benzoylcholine hydrolyzing activity of serum cholinesterase, we conclude from the data that dipeptidyl peptidase IV was the true Lys-Pro-p-nitroanilide cleaving activity. Furthermore, the conclusion can also be drawn that hydrolysis of substance P reported by Lockridge 1982 is caused by the contamination that cannot be completely separated from the esterase during the purification method used.

Cholinesterases↗