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Biomedical subjects

S Blumberg

Publications and source records attributed to S Blumberg.

At least 55 records · Page 3Linked to original sources
PubMed1983

Inhibition of metalloendopeptidases by 2-mercaptoacetyl-dipeptides.

A series of 2-mercaptoacetyl-dipeptides, a potential group of metalloendopeptidase inhibitors, has been synthesized by coupling the N-hydroxysuccinimide ester of S-acetyl-2-mercaptoacetic acid with hydrophobic dipeptide methyl ester hydrochlorides, followed by hydrolysis with NaOH in aqueous methanol and acidification with HCl. Thus, the 2-mercaptoacetyl derivatives of L-phenylalanyl-L-leucine, L-leucyl-L-phenylalanine and L-leucyl-D-phenylalanine were prepared. The first two compounds inhibit effectively thermolysin from Bacillus thermoproteolyticus and a metalloendopeptidase isolated from Streptomyces griseus, with Ki values in the micromolar range or below. The third compound inhibits the two enzymes only poorly, showing the stereospecificity of the inhibition process. These inhibitors should provide a useful tool for the study of bacterial and mammalian metalloendopeptidases (or dipeptidyl carboxypeptidases) and for the assessment of their physiological role.

Chemical Phenomena↗
PubMed1983

Protection of enkephalins from enzymatic degradation utilizing selective metal-chelating inhibitors.

Metal ion-chelating agents inhibited enkephalin degradation by a rat striatal membrane-associated endopeptidase termed 'enkephalinase'. The combination of a hydrophobic dipeptidyl moiety and a transition metal-chelating moiety in the same molecule resulted in very efficient and selective inhibitors of enkephalinase. The mercaptoacetyl dipeptides (2-mercaptoacetyl-Leu-Phe and 2-mercaptoacetyl-Phe-Leu) and the N-phosphorylated dipeptides (phosphoryl-Leu-Phe and phosphoramidon) inhibited enkephalinase with IC50 values of 15, 70, 0.3 and 1 nM respectively, but were much less potent against the aminopeptidase and angiotensin converting enzyme, two other metalloenzymes implicated in the degradation of the enkephalins in brain. The inhibition of enkephalinase, using phosphoryl-Leu-Phe as a selective inhibitor, resulted in a 4 fold increase in the amount of enkephalin recovered following K+ depolarization of rat striatal slices.

Aminopeptidases↗
PubMed1983

Structure-activity relationship in the mast cell degranulating capacity of neurotensin fragments.

The mast cell degranulating capacity of neurotensin and three of its fragments was examined. In Tyrode solution (137 mM NaCl, 2.7 mM KCl, 0.4 mM NaH2PO4, 1.4 mM CaCl2, 1 mM MgCl2, 10 mM Hepes, 5.6 mM glucose, pH 7.4), neither intact neurotensin nor its C-terminal tripeptide (Tyr-Ile-Leu) caused any release of histamine. Concentrations of neurotensin exceeding 10(-4)M did cause histamine release but through lysis of the cells. The C-terminal hexa- and octapeptides of neurotensin (Arg-Arg-Pro-Tyr-Ile-Leu and Lys-Pro-Arg-Arg-Pro-Tyr-Ile-Leu, respectively) induced a non-cytolytic release of histamine with the latter peptide being more active (ED50 = 90 microM for the hexapeptide and 13 microM for the octapeptide). This release was not affected by the C-terminal tripeptide. It was found to be calcium-dependent and was inhibited by the anti-allergic drug, disodium cromoglycate. Phosphatidylserine did not enhance release of histamine and saturation of the immunoglobulin E (IgE) receptors did not inhibit it.

Animals↗
PubMed1983

Specific inhibition of Pseudomonas aeruginosa elastase injected intracorneally in rabbit eyes.

The compounds benzyloxycarbonyl-L-leucyl-hydroxamate (Z-Leu-NHOH), phosphoryl-L-leucyl-L-phenylalanine (P-Leu-Phe) and 2-mercaptoacetyl-L-phenylalanyl-L-leucine (HSAc-Phe-Leu) strongly inhibit the activity of Pseudomonas elastase in vitro. The capacity of these inhibitors to prevent corneal melting and perforation due to the elastase was examined in rabbit eyes by intrastromal injections of elastase solutions containing the various inhibitors. HSAc-Phe-Leu was substantially more effective than the other two inhibitors. It completely prevented corneal perforation, markedly delayed the appearance of melting and kept the degree of melting at a minimum. Subconjunctival injections of HSAc-Phe-Leu given prior to enzyme administration delayed but did not prevent corneal melting or perforation, whereas frequent topical application with drops of this inhibitor completely prevented corneal melting. It is suggested that HSAc-Phe-Leu or similarly structured inhibitors of the elastase might be helpful in the management of corneal infections with Pseudomonas aeruginosa.

Administration, Topical↗
PubMed1982

Enhancement of phagocytosis by neurotensin, a newly found biological activity of the neuropeptide.

Specific binding of neurotensin (NT) to mouse peritoneal thioglycollate-elicited macrophages and macrophages differentiated in vitro from bone marrow cells was demonstrated and characterized. NT binding to these phagocytes modulated their phagocytic capacity in a biphasic manner. At concentrations of 10(-14) to 10(-9) M NT, a dose-dependent augmentation of phagocytosis (up to 2-fold) was observed. Further increases in the concentration of NT resulted in a gradual decrease of the augmented response until the basal phagocytic activity (in the absence of NT) was reached. Three partial sequences of NT, NT (8-13), NT (6-13) and NT (1-10), were also effective in augmenting the phagocytic response of thioglycollate elicited macrophages, but the maximal effect was attained at about 10(-7) M and stayed at that level up to a concentration of 10(-5) M. The activity of the three NT partial sequences was comparable to that of substance P and tuftsin. Scatchard analysis of (3H)NT binding to macrophages suggested the existence of two populations of binding sites, a major population of relatively low affinity binding sites and a small population of high affinity binding sites. NT (8-13), NT (6-13), substance P and tuftsin competed with (3H)NT binding to the low affinity sites with a comparable KI to that of NT. NT (1-10) did not compete for the binding at the low affinity sites. It is suggested that NT binding to the high affinity sites leads to enhancement of phagocytosis, whereas its binding to the low affinity sites leads to inhibition of the augmented response. However, the low affinity sites are the sites of interaction of NT (8-13), NT (6-13), substance P and tuftsin with the phagocytes and their saturation with the peptides leads to augmentation of phagocytosis.

Amino Acid Sequence↗
PubMed1982

In vitro inhibition of Pseudomonas aeruginosa elastase by metal-chelating peptide derivatives.

Pseudomonas aeruginosa elastase is a zinc metalloendopeptidase, probably responsible for the tissue destruction observed during infections with this organism. The elastase of a virulent Pseudomonas aeruginosa strain (Habs serotype 1) was isolated and found to have a molecular weight of 35,000; it readily degraded elastin and cartilage proteoglycans. A series of amino acid and peptide derivatives containing the metal-chelating moieties hydroxamate, phosphoryl, or thiol were synthesized and tested as potential inhibitors of the enzyme. Inhibition constants (K(i)s) for the compounds were determined with the chromophoric substrate furylacryloyl-glycyl-l-leucyl-l-alanine. The hydroxamic acid derivatives of benzyloxycarbonyl-glycine, benzyloxycarbonyl-l-leucine and benzyloxycarbonyl-l-phenylalanine had inhibition constants in the range of 11 to 28 muM. The 2-mercaptoacetyl derivatives of l-leucyl-d-phenylalanine and l-leucyl-l-phenylalanine had K(i) values of 34 and 1.5 muM, respectively, demonstrating the stereospecificity of the inhibition. The most potent inhibitors tested were 2- mercaptoacetyl-l-phenylalanyl-l-leucine and phosphoryl-l-leucyl-l-phenylala-nine (K(i) = 0.2 muM). Similar compounds lacking the metal-chelating moiety were about 3 orders of magnitude poorer inhibitors. When the inhibition of the enzyme activity towards azocasein, elastin, or cartilage was examined, inhibitor concentrations approximately 50-fold higher than the respective K(i)s were required to obtain 60 to 90% inhibition. Virtually complete inhibition was achieved with these substrates at inhibitor concentrations 500-fold higher than the respective K(i)s (0.1 to 14 mM). Although, 2-mercaptoacetyl-l-phenylalanyl-l-leucine and phosphoryl-l-leucyl-l-phenylalanine exhibited the same affinity to the enzyme, the latter was inferior in inhibiting cartilage proteoglycan degradation. 2-Mercaptoacetyl-l-phenylalanyl-l-leucine represents a class of potent elastase inhibitors that might prove useful in the management of P. aeruginosa infections.

Cartilage↗
PubMed1982

Inhibition of enkephalin degrading enzymes by metal chelating reagents.

The N-phosphorylated dipeptide K2PO3-Leu-Phe (P-Leu-Phe) and the mercaptoacetylated dipeptides SHCH2CO-Leu-Phe and SHCH2CO-Phe-Leu are potent inhibitors of the enkephalin carboxydipeptidase (enkephalinase) activity from rat striatal synaptosomal membranes; IC50, 0.3 nM, 15 nM, and 70 nM, respectively. These metal chelating compounds also inhibit the enkephalin degrading aminopeptidase activity present in the soluble fraction of rat striatum, although higher concentrations of inhibitors are needed; IC50, 100 microM, 80 microM and 150 microM, respectively. The binding of Leu-enkephalin (Leu-Enk) to rat striatal synaptosomal membranes is enhanced when the enkephalinase activity or the aminopeptidase activity present in these membranes is inhibited. Higher binding is obtained when both enzymes are inhibited. Similarly, the inhibition of these activities in rat striatal slices, using either puromycin or secobarbital which inhibit the aminopeptidase and enkephalinase, respectively, increases the amount of enkephalin recovered following K+ depolarization by about 100 percent. P-Leu-Phe at 1 mM, a concentration which inhibits both enzymatic activities, increased the amount of enkephalin recovered by 10-fold. The intracerebroventricular administration of 60 micrograms P-Leu-Phe with 200 micrograms of Leu-Enk induced analgesia in 4 out of 5 rats while Leu-Enk alone was not effective.

Aminopeptidases↗
PubMed1981

Distinct classes of substance P receptors revealed by a comparison of the activities of substance P and some of its segments.

The contracting potency of Substance P and of its C-terminal fragments was studied using four isolated preparations of smooth muscle. The Substance P receptors in the four muscles studied can be differentiated on the basis of their interactions with Substance P and its C-terminal fragments. On the guinea pig ileum, the potency of Substance P is equal to that of the C-terminal octa- and heptapeptide segments and in the rat ileum the potency of Substance P is equal to that of the C-terminal octapeptide and even higher than that of the heptapeptide. In contrast, on the cow pupillary sphincter and guinea pig urinary bladder, Substance P is markedly less potent that the C-terminal octa-, hepta- and hexapeptides. These results suggest the existence of different classes of Substance P receptors and indicate that the N-terminal sequence may be important in regulating Substance P activity.

Animals↗
PubMed1981

In vitro contraction of the pupillary sphincter by substance P and its stable analogs.

The effects of substance P and substance P analogs have been studied quantitatively by use of an isolated preparation of bovine pupillary sphincter muscle. Substance P contracts the pupillary sphincter in a dose-dependent manner with a value for median effective dose (ED50) of 1.0 X 10(-6) M. The effects of substance P result from its interaction with a specific receptor in the pupillary sphincter. These results strengthen the view that substance P is involved in the oculopupillary reflex.

Animals↗