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Biomedical subjects

D Brandenburg

Publications and source records attributed to D Brandenburg.

At least 91 records · Page 5Linked to original sources
PubMed1982

[LeuB24]- and [LeuB25]insulins are not antagonists of lipogenesis in adipocytes.

Semisynthetic human [LeuB24]-and [LeuB25]insulins were investigated to determine whether they show antagonistic properties towards insulin-stimulated lipogenesis in isolated fat cells. In contrast to other reports, we could detect only an additive agonistic effect when constant concentrations (e.g. 0.3 ng/ml) of the analogues were mixed with varying concentrations of insulin, or when constant concentrations (e.g. 0.3 ng/ml, 0.6 ng/ml) of insulin were mixed with varying concentrations of the analogues. Similar results were obtained with mixtures of insulin and NA2-acetyl- or NA2-propionyl-des-GlyA1-insulins. These results do not support the contention that a diabetic state could be caused by either of these mutant human insulins.

Adipose Tissue↗
PubMed1982

Preparation and properties of covalently linked insulin dimers.

The synthesis of six isomeric insulin dimers, linked through selected amino groups of the monomers by a dicarboxylic acid, is described. Symmetrical dimers were obtained by direct crosslinking of N,N-bis(methylsulfonyl-ethoxycarbonyl)insulins with the bis(p-nitrophenyl) esters of dicarboxylic acids. The synthesis of asymmetrical dimers was achieved by use of Msc-protected insulin active ester intermediates. N epsilon-B29,N epsilon B29'-Insulin dimers containing oxalyl, suberoyl and dodecanedioyl crosslinks were produced. N alpha B1,N epsilon B29'-Insulin dimers were suberoyl and dodecanedioyl crosslinks were synthesized; all other dimers were synthesized with suberoyl crosslinks. The positions of crosslinks were determined by sulfitolysis, tryptic digestion, electrophoresis and quantitative end-group determination. The dimers showed potencies between 1-60% that of insulin on a weight basis in stimulating lipogenesis in isolated fat cells. The potencies are considerably lower than the relative binding affinities determined with isolated fat cells.

Adipose Tissue↗
PubMed1981

Hydrodynamic characterization of the photoaffinity-labeled insulin receptor solubilized in Triton X-100.

The insulin receptor in isolated rat liver plasma membranes was covalently labeled with the photoreactive insulin analogue NB-29-[(4-azido-2-nitrophenyl)acetyl]insulin and solubilized with the nondenaturing detergent Triton X-100. The resulting protein-detergent complex was characterized by gel filtration on Sepharose 6B, sedimentation rate determination in linear sucrose gradients, and equilibrium isopycnic centrifugation in NaBr and CsCl. The labeled insulin receptor was found in two forms. The Strokes radii and s20,w's of the two receptor-detergent complexes (R1 and R2) were (mean +/- SEM) 7.08 +/- 0.04 and 3.62 +/- 0.05 nm and 10.45 +/- 0.04 and 6.54 +/- 0.15 S, respectively. The two forms appeared to have the same buoyant density, 1.285 +/- 0.002 g cm-3. The dissociation of R2 from R1, or its reaggregation, either with itself or with other unlabeled proteins, to give R1 proceeded without chemical modification. Mild reduction of disulfide bonds (1 mM 1,4-dithiothreitol) increased the dissociation of R2 from R1. These results indicate that the solubilized receptor binds significant amounts of detergents, that the insulin binding component of the receptor binds to other receptor components by hydrophobic interactions, and that one or more components of the insulin receptor contain intrachain disulfide bonds.

Affinity Labels↗
PubMed1981

Mechanism of action of insulin and insulin analogues. A comparison of the hepatic and peripheral effects on glucose turnover of insulin, proinsulin and three insulin analogues modified at positions A1 and B29.

A [14C]-glucose tracer infusion method was used to compare the effects of insulin infusion on glucose metabolism with the effects of infusion of three semisynthetic modified insulins and of proinsulin. Insulin produced hypoglycaemia in the anaesthetised dog by decreasing hepatic glucose production and increasing peripheral glucose utilisation. Compensatory antihypoglycaemic mechanisms eventually modified these responses. A1, B29-Diacetyl insulin exerted an hypoglycaemic effect entirely by stimulation of peripheral glucose uptake. A1-B29 crosslinked insulins and proinsulin produced hypoglycaemia almost entirely by decreasing hepatic glucose production and had little effect on tissue uptake. These observations suggest that insulin analogues may have actions in vivo that are qualitatively different from those of native insulin and suggest that certain analogues have a predominant action on the liver. This has important therapeutic implications concerning the development of semisynthetic insulins for clinical use.

Animals↗
PubMed1981

Chronic intestinal pseudo-obstruction.

Intestinal pseudo-obstruction (IP) is an uncommon disorder of gut motility which must be differentiated from mechanical intestinal obstruction. We have seen 11 such patients over the last 5 years. Characteristic symptoms, shared by mechanical obstruction, include abdominal distention and pain, nausea, and vomiting. Radiologic studies reveal dilated loops of bowel with air fluid levels. In most patients a major differentiating feature from obstruction may be the presence of diarrhea rather than obstipation. Steatorrhea is secondary to an overgrowth of anaerobic bacteria in the motionless dilated loops of bowel. IP has been associated with various disorders: in our series two patients had scleroderma, one multiple small bowel diverticula, one systemic amyloidosis, one celiac disease, and one spinal cord injury; in only two patients was the disorder considered "idiopathic." Three patients had previously undergone a jejuno--ileal bypass for morbid obesity. During the acute episode, the patients were treated symptomatically with decompression by nasogastric or rectal tube with fluid and electrolyte replacement. Malabsorption treated with broad spectrum antibiotics reversing the steatorrhea but not episodes of pseudo-obstruction. Magnesium deficiency was present in seven patients and its correction resulted in amelioration of the symptom complex. In two patients episodes of pseudo-obstruction were markedly reduced by metoclopramide which was not effective in two others.

Adult↗
PubMed1981

Two mutant forms of human insulin. Structural consequences of the substitution of invariant B24- or B25-phenylalanine by leucine.

In 1979 the first abnormal human insulin was discovered. With the minute samples from the patient a Phe leads to Leu replacement could be established in either position B24 or B25. For the unequivocal localization of the substitution both the Leu analogues had to be prepared by semisynthesis. While another laboratory did this with the sequence of porcine insulin, here we are dealing with the true analogues of human insulin. In the present paper the structural consequences of the substitutions are investigated. Human insulin obtained by total synthesis served as a reference. Its CD spectral properties are herewith documented. According to the substantial deviations of the CD spectrum of [Leu B24]insulin, the introduction of the new side-chain forces conformational changes to occur not only in its immediate surrounding but also in the peptide chain. The failure to give the typical CD spectral response to variations of protein and zinc concentration indicates that the ability to form quaternary structure is impaired. Though dimerization was confirmed by gel chromatography to be largely reduced, it is concluded that, in addition, interactions normally responsible for the increase in tyrosine-CD with association are weakened. [Leu B25]insulin, on the other hand, does exhibit all CD spectral effects characteristic of the native hormone, though quantitatively somewhat reduced. The CD spectroscopic results are in full agreement with the computergraphic analysis of the sterical consequences of the substitutions. For B24-leucine an acceptable packing without movements of the mainchain and/or B15-leucine and without affecting dimerization is impossible, whereas B25-leucine can be accommodated without causing bad contacts either in the monomer or in the dimer. The structural results do not explain why [Leu B25]-insulin should have a lower biological activity than the B24 analogue, 2.1 +/- 0.3% versus 20.9 +/- 2.8%, in the fat cell test. They suggest, however, an important but not critical stereospecific role for the B25-phenylalanine in binding.

Circular Dichroism↗
PubMed1981

The resistance of crosslinked insulin derivatives to pepsin and trypsin.

The introduction of a crosslink between the amino groups of A1-glycine and B29-lysine of the insulin molecule leads to a marked decrease in sensitivity towards pepsin. Under conditions where insulin is completely degraded over 70% of N alpha A1, N epsilon B29-(carbonyl-bis-methionyl) insulin [OC(Met)2] remain intact. The resistance increases with the length of the crosslink, i.e. oxalyl less than OC(Met)2 less than dodecanedioyl insulin. The carbonyl-bis-methionyl derivative is also stabilized against tryptic attack, but to a smaller degree.

Animals↗
PubMed1981

Intramolecular enzymatic peptide synthesis: trypsin-mediated coupling of the peptide bond between B22-arginine and B23-glycine in a split crosslinked insulin.

The resealing of a split peptide bond (B22/23) in a crosslinked insulin derivative by a trypsin-mediated coupling reaction in Tris buffer/glycerol/dimethylsulphoxide 1 : 1 : 1 at pH 6.5 is described. The coupling yield obtained with N alpha A1, N epsilon B29-(carbonyl-bis-methionyl) insulin [OC(Met)2] was 55-60%, and reproducible yields of OC(Met)2-insulin were 40%. After removing the crosslink and purification, crystalline resynthesized insulin of high biological activity was obtained in a yield of 43% and an overall yield, based on split OC(Met)2-insulin, of 18%.

Animals↗
PubMed1981

Iodinated [A1-N gamma-(4-azidophenylacetyl)-D-alpha, gamma-diaminobutyric acid]insulin: its preparation and properties.

The synthesis of a photo-sensitive analogue of pork insulin (A1-N gamma-(4-azidophenylacetyl)-D-alpha, gamma-diaminobutyric acid]insulin is reported. It could be shown that this analogue forms specific cross-links to binding proteins on irradiation with UV light. Furthermore, it was shown that the photo-label itself was not iodinated, nor did it influence the normal distribution of iodination. It can be concluded that this derivative bears all of the characteristics necessary for specifically labeling membrane-bound receptors.

Adipose Tissue↗
PubMed1981

[An improved method for the combination of modified insulin chains (author's transl)].

A procedure is described in which the yields of the combination of insulin A and B chains, especially of modified chains, are increased. The chains are reduced simultaneously in 8M urea buffer at pH 8.6 with 2-mercaptoethanol. The thiol chains are not isolated but transferred to the oxidation buffer at pH 10.6 by means of gel chromatography on Sephadex G-25. During the chromatography about 50% of the tetrathiol A chain is oxidized specifically to a dithiol A chain disulphide, in which presumably the 6,11-disulphide ring is closen. Generally we observed that the combination yields of modified A or B chains are lower than the yields of combinations of unmodified A or B chains. It seems that there is a correlation between the biological activity of the analogue and the yield obtained by the recombination of the chains.

Chemical Phenomena↗
PubMed1980

Covalent linking of photoreactive insulin to adipocytes produces a prolonged signal.

The first step of insulin's many cellular functions is specific binding to receptors on the plasma membrane of target cells. The subsequent molecular basis of insulin action, particularly the coupling mechanism(s) involved in transmitting the biological message, remains largely unknown. Our approach to the problem centres on the application of a series of well characterized photo-insulins carrying an aryl-azido or nitro-aryl-azido group in positions A1, B1, B2 or B29 (refs 2--4). Specific binding to membrane components could be demonstrated with B1-, B29- (ref. 5) and A1-photo-insulins as well as a B2-derivative. We now report that lipogenesis is increased to, and maintained at, near-maximal levels for several hours after photoinduced covalent binding of B2- (2-nitro,4-azidophenylacetyl)-des-PheB1-insulin (Napa-DP-insulin) to living adipocytes.

Adipose Tissue↗
PubMed1980

Radioimmunoassay of chemically modified insulins.

The reactions between four insulin antisera and eighteen insulin derivatives with modifications at the A1, B1 and B29 positions have been studied using a standard double-antibody radioimmunoassay procedure. The derivatives studied had: a) single modifications at A1, B1 or B29,; b) modifications at two sites with or without a crosslink between them; c) modifications at all three sites with or without a crosslink. Analysis of the results showed a clear difference in the reactivity of the antisera. One antiserum (GP5) was highly sensitive to modifications of the B1 residue and another (Ab1) was sensitive to A1 and B29 modifications. Thus, immunological potencies of insulin analogues derived on the basis of these reactions with the antisera give widely varying results. These antisera were used in discriminatory radioimmunoassays of chemically modified insulins in biological fluids for estimation of in vivo hypoglycaemic potencies by an infusion technique, where the knowledge of the specificity of the antisera was useful in assessing the immunological identity of immunoreactive material in plasma with the analogue infused.

Adipose Tissue↗
PubMed1979

Insulin action on adipocytes. Evidence that the anti-lipolytic and lipogenic effects of insulin are mediated by the same receptor.

1. The dose-response relationships of insulin stimulation of lipogenesis and inhibition of lipolysis were studied simultaneously by using rat adipocytes to determine whether these different effects of insulin are mediated through the same or different sets of receptors. 2. The sensitivity (defined as the concentration of insulin required to produce a half-maximal effect) of the stimulated lipogenic response to insulin was not significantly different from the sensitivity of the anti-lipolytic response to insulin. The addition of different adrenaline and glucose concentrations did not alter the half-maximal concentration of insulin required to inhibit lipolysis. 3. The specificities of the lipogenic and antilipolytic responses were studied by using insulin analogues. The sensitivities of the lipogenic and anti-lipolytic responses were the same for five chemically modified insulins and hagfish insulin, which have potencies compared with bovine insulin of between 3 and 90%. 4. Starving rats for 48h significantly increased the sensitivities of both the antilipolytic and lipogenic responses to insulin, but the changes in the sensitivities of both lipogenesis and anti-lipolysis returned to that of fed rats. 5. We conclude that insulin stimulates lipogenesis and inhibits lipolysis over the same concentration range. These observations provide powerful evidence that the different effects of insulin are mediated through the same set of receptors.

Adipose Tissue↗
PubMed1979

[Preparation of N,N-bis(methylsulphonylethoxycarbonyl)insulins (author's transl)].

The preparation of N,N-bis(methylsulfonylethoxycarbonyl)insulins is described. In an aequeous buffer at pH 5.8 selectivity of the reaction of insulin with 20 equivalents of N-(methysulfonylethoxycarbonyloxy)succinimide (Msc-ONSu) leads very specifically to N alpha A 1,-N alpha B 1-(Msc)2 - insulin. The product can be isolated in a yield of 60%. Using N alpha A 1-citraconylinsulin the N alpha B 1, NEB29-(Msc)2 -insulin can be prepared in a yield of 40% based on insulin.

Biological Assay↗
PubMed1979

[Synthesis of the fragments A1-8, A1-7, A9-15 and A8-15 of the chicken insulin A chain (author's transl)].

By coupling the peptide derivatives H-Cys(SBut)-Cys(SBut)-His-OMe(6-8 b) and H-Cys(SBut)-Cys(SBut)-OH(6-7b) respectively with Trt-Gly-Ile-Val-Glu(OBut)-Gln-OH(1-5a) the N-terminal sequences A1-8 and A1-7 of the chicken insulin A chain have been prepared. The sequence of A9-15 has been obtained by connecting Bpoc-Asn-Thr(But)-Cys(SBut)-OH (9-11c) and H-Ser(But)-Leu-Try(But)-Gln-OH (12-15). Acylation of the aminopeptidderivative 9-15b with Bpoc-N2H3 yielded fragment A8-15 (8-15).

Animals↗