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K Neubert

Publications and source records attributed to K Neubert.

103 records · Page 6Linked to original sources
PubMed1980

[Structure-activity relationship in the enzymatic hydrolysis of dipeptide aryl amides by dipeptidyl peptidase IV].

Quantitative structure activity analysis of the substrate types Ala-Ala-AR and Ala-Pro-AR containing different substituents in the aryl ring showed that the rate-limiting step in the hydrolysis of the alanine substrates by dipeptidyl peptidase IV occurs in th acylation reaction (kcat approximately k2). Probably, the tetrahedral intermediate of the acylation process has a real life time. The positive q-value of the Hammett-equation in k'cat suggests that the N-atom of the arylamide is charged more negatively in the transition state TI not equal to than in the original state TI. The analysis of the quantitative conformation activity relationship (QCAR) gives information on the steric situation in the tetrahedral intermediate of the acylation step near the transition state. The rate limiting step in the hydrolysis of the substrates of the proline type occurs in the deacylation reaction.

Dipeptides↗
PubMed1979

[Studies of the consecutive hydrolysis of dipeptidyl-4-(phenylazo)-phenylamides by an aminopeptidase from Brassica napus].

The relatively alanine-specific amino peptidase from Brassica napus hydrolyzes dipeptidyl-4-(phenylazo)-phenylamide according to a consecutive mechanism. Enzyme-kinetic studies of dipeptidyl-4-(phenylazo)-phenylamides carried out by means of spectrometrical procedures of measurement are only possible when the increase in the concentration of the fission product p-aminoazobenzene is recorded. For assessing the kinetic parameters of the intermediary steps of the hydrolysis of dipeptidyl-4-(phenylazo)-phenylamides a function is derived describing the dependence of the concentration of fission products of p-aminoazobenzene on reaction time. The satisfactory correspondence of the kinetic parameters calculated for the intermediary-originating substrate L-ala-4-(phenylazo)-phenylamide as substrate demonstrates the applicability of the procedure described in the present paper.

Aminopeptidases↗
PubMedDate not supplied

Derivatives of beta-casomorphins with high analgesic potency.

Beta-casomorphin (5) Tyr-Pro-Phe-Pro-Gly, a partial sequence of bovine beta-casein with moderate opioid properties and mu-receptor affinity, was modified by substituting for the natural L-amino acids their D-analogs, and D-pipecolic acid, as well as by amidation of the C-terminal. Substitution of D-Pro or D-pipecolic acid for L-Pro4 considerably increased the analgesic action and the potency on guinea-pig ileum of beta-casomorphin (5) as well as of casomorphin [4] amide. The resulting D-Pro4 analogs Deprolorphin and Deproceptin which showed high analgesic potency after both intracerebroventricular and intravenous administrations. Also, the substitution of D-Phe for L-Phe3 enhanced, even though to a lesser degree, the antinociceptive action. Both naltrexone and naloxone completely blocked the effects in vivo and in vitro. The substitution of D-Pro for L-Pro2 abolished the opioid-like actions, while substituting D-pipecolic acid for L-Pro2 resulted in an increased analgesic effect of remarkably long duration. The correlation of analgesic action with the effects on isolated organs separates the L-Pro4-substituted derivatives and D-Phe3-CM(5) from the other modified casomorphins and morphine, indicating that the analgesic potency of the former was about ten times that of the latter group in the case of identical GPI-potency. This may involve different subpopulations of opiate mu-receptors.

Amino Acid Sequence↗
PubMedDate not supplied

Opiate receptor binding affinities of some D-amino acid substituted beta-casomorphin analogs.

beta-Casomorphin-(5) and some analogs modified by the introduction of some D-amino acids and D-pipecolic acid as well as by C-terminal amidation were tested for their affinities to mu- and delta-binding sites in rat brain membranes. The binding affinities of these compounds are compared with the known activities in the guinea pig ileum (GPI) and mouse vas deferens (MVD) test and their antinociceptive potencies in rats. The substitution of D-proline for proline in position 4 in beta-casomorphin-(5) and beta-casomorphin-(4)amide (morphiceptin) results in derivatives with very high mu-binding affinity and mu-selectivity. These affinities correspond to the respective analgesic potencies. Both binding to mu-receptors and analgesic potency are also enhanced by the introduction of D-Phe in position 3. Testing D-Ala2 substituted derivatives with respect to their ability to compete for 3H-naloxone, we observed apparent differences between the pentapeptide amides (biphasic displacement curves) and the tetrapeptide amides (monophasic displacement curves). The substitution of L-Pro2 by D-pipecolic acid yields an analog with preferential delta-receptor affinity in the organ preparations (MVD) but preferential mu-receptor affinity in brain membranes. This finding suggests a possible difference between peripheral and central mu-binding sites.

Amino Acids↗
PubMedDate not supplied

Nonopioid effects of beta-casomorphin-5 in guinea pig heart: alterations to the beta-adrenoceptor-G-protein complex and inhibition of myocardial responses to isoproterenol.

The influence of beta-casomorphin-5 on the beta-adrenoceptor complex in guinea pig heart membranes was studied by means of binding studies, G-protein investigations and isolated heart preparations. In nanomolar concentrations beta-CM-5 induced an increase in receptor affinity towards the agonist isoproterenol whereas the antagonist affinity was reduced. The isoproterenol-stimulated increase in cardiac contractility, moreover, is reduced by 10 nM beta-CM-5. Furthermore, beta-CM-5 was found to inhibit the isoproterenol-induced GDP/GTP exchange as well as the [35S]GTP[S] binding to guinea pig heart membranes, indicating an involvement of G-proteins. These findings suggest that low concentrations of beta-CM-5 modulate the functional properties of the myocardial beta-adrenoceptor-G-protein complex, presumably resulting in its desensitization. The observed effects of beta-CM-5 are not prevented by naloxone and, therefore, are nonopioid in nature.

Amino Acid Sequence↗
PubMedDate not supplied

Structure-activity relationships of cyclic beta-casomorphin-5 analogues.

Cyclic analogues of the beta-casein-derived opioid peptide beta-casomorphin-5 (H-Tyr-Pro-Phe-Pro-Gly-OH) were prepared through substitution of the Pro2 residue with various alpha,omega-diamino acid residues (lysine, ornithine, 2,4-diaminobutyric acid) and cyclization of the omega-amino group to the C-terminal carboxyl function. Compounds of this type, with D-configuration at the 2-position residue, showed high opioid receptor affinity with some preference for mu receptors over delta receptors, high potency in the guinea pig ileum assay and considerable activity in the mouse vas deferens assay. Configurational inversion at the 4-position in these cyclic analogues resulted in enhanced affinity for both mu and delta receptors, whereas N-methylation of the Phe3 residue produced a potency decrease.

Amino Acid Sequence↗
PubMedDate not supplied

Linear and cyclic beta-casomorphin analogues with high analgesic activity.

We investigated the antinociceptive efficacy of casomorphin (CM) derivatives using the vocalization test. Male Wistar rats received chronic microcannulae into the right lateral ventricle. One week later we examined the analgesic effect of CM derivatives 10, 30, 60, and 90 min after intraventricular injection (5 microliters). The analgesic effect was calculated as the individual percent increase in the pain threshold and was compared to controls (saline treatment). The substitution of D-lysine and D-ornithine in position 2 in connection with a cyclization through ring closure of the 2 position side chain amino group to the C-terminal glycine-COOH group resulted in high analgesic potency. The substitution of D-Pro4 was without any effect in the ineffective linear derivatives and decreased the effectiveness in the highly effective cyclic derivatives. The cyclic [D-Orn2]CM-5 and the cyclic [D-Lys2]CM-5 are the CM derivatives with the highest antinociceptive activity. The cyclic [D-Orn2]CM-5 is greater than 1000 times more effective than morphine. We conclude, on the basis of studies of receptor binding and in vitro investigations, that mu receptor activity alone is not responsible for the analgesic activity. The delta receptor and possibly also the kappa receptor could modulate the nociceptive effectiveness.

Amino Acid Sequence↗