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Biomedical subjects

D Brandenburg

Publications and source records attributed to D Brandenburg.

At least 109 records · Page 6Linked to original sources
PubMed1979

[Synthesis of (LysA13)bovine insulin A chain analogs as (Lys(Tfa)A13)A(SO3H)4 and Nalpha-A1-Msc-(LysA13)A(SO3H)4 derivatives using the S-tert-butylmercapto residue for thiol protection (author's transl)].

The following paper describes the synthesis of the [LysA13]bovine insulin A chain analog as [Lys(Tfa)A13]A(SO3H)4 and NalphaA1-Msc-[LysA13]A(SO3H)4 derivatives using the S-tert-butylmercapto residue for thiol protection. Although the intermediate S-tert-butylmercaptocysteinyl-peptide derivatives showed a good solubility in organic solvents the resulting fully protected A chain derivatives had a poor solubility in organic solvents and therefore were deblocked converted into the tetra(S-sulfonic acid) derivatives and purified via ionexchange chromatography.

Animals↗
PubMed1977

Crosslinked insulins: preparation, properties, and application.

Crosslinked insulins have proved to be valuable for structure-function studies and as proinsulin models. In the first part of the paper, a short review of the literature on analytical investigations, the preparation of A1-B1- and A1-B29-crosslinked derivatives, their biological activities in vivo and in vitro, and CD-spectral properties is given. The results of reduction/reoxidation studies with insulin derivatives containing irreversible and cleavable crosslinks are summarized. In the second part, new A1-B29-crosslinked monomers and 3 symmetrical dimers, linked between A1-A'1, B1-B'1 and B29-B'29, are described, as well as some results of tritium-labelling and of enzymatic degradation experiments with A1-B29-linked insulins.

Amino Acid Sequence↗
PubMed1977

Studies on the relationship between the molecular structure and the catabolism of insulin.

The catabolism of insulins modified at the A1, B1 or B29 positions or containing a synthetic crosslink between the A1 and B29 positions has been studied in vivo and in vitro. The metabolic clearance rates (MCR) of insulin, proinsulin and chemically modified insulins have been measured by a priming-dose constant infusion technique in greyhounds. Insulins modified at A1 and B29, particularly the crosslinked materials, had markedly lowered MCR's whilst B1 analogues did not differ from insulin. Proinsulin and the A1-B29 crosslinked materials showed a markedly lowered degradability by glutathione-insulin transhydrogenase.

Animals↗
PubMed1976

Receptor-binding region of insulin.

X-ray analysis, circular dichroism, receptor binding and biological potencies of chemically modified insulins suggest that the conformation of the insulin molecule is critical to the formation of both the zinc insulin hexamer and the insulin-receptor complex. Results are consistent with an insulin receptor-binding region including many of the hydrophobic residues important to dimerisation in addition to more polar surface residues. There is a further possibility of formation of an antiparallel sheet structure between the insulin and receptor molecules in the complex similar to that between monomers in the insulin dimer.

Adipose Tissue↗
PubMed1976

Biological properties of chemically modified insulins. I. Biological activity of proinsulin and insulin modified at A1-glycine and B29-lysine.

Beef insulin, pork proinsulin and four derivatives of beef insulin modified at the A1-B29 site on the molecular surface have been studied. Three derivatives had a synthetic crosslink between the A and B chains. Previous studies with these materials [2, 3 and 5] had demonstrated in vivo bioactivities which were much higher than those displayed in vitro. This paper reports experiments which explain this discrepancy. The analogues were administered at equimolar rates to anaesthetised greyhounds by a priming-dose constant infusion technique and the plasma concentrations achieved were estimated by radioimmunoassay. Proinsulin and the modified insulins were metabolised more slowly than insulin. Biopotency values, which related fall in plasma glucose concentration to the total administered dose of analogue, agreed broadly with published results of conventional in vivo bioassays. On the other hand, calculation of potency in relation to the serum concentration of analogue actually achieved, yielded results which agreed more closely with in vitro assay data. We conclude that for these analogues, reported discrepancies between in vitro and in vivo biopotencies can be largely explained by the different rates at which these materials are metabolised.

Adipose Tissue↗
PubMed1975

[Insulin analogues with permuted A chain N-terminus (author's transl)].

By partial synthesis insulin analogues were prepared in which the amino acid in position 1 of the A chain was permuted. Glycine in position A 1 was exchanged for leucine, tert.- butyloxycarbonylvaline, valine, proline, lysine as well as glutamic acid. Two pathways of partial synthesis were followed: Firstly, des-1-glycine-A-chain S-sulfonate was reacted with active esters of tert.-butyloxycarbonylamino acids. The ensuing modified A-chains were combined with natural B-chain to give A1-permuted insulins. In the second procedure, the preparation of tris-Boc-[A1-leucine]insulin was accomplished by reaction of Boc-leucine N-hydroxysuccinimide ester with NalphaB1,NepsilonB29-bis(tert.-butyloxycarbonyl)-des-A1-glycine-insulin. The protected insulin derivative had been prepared by combination of des-glycine-A-chain with Nalpha1,Nepsilon29-bis(tert.-butyloxycarbonyl)-B-chain. The deprotected analogues differed considerably in their CD-spectra from insulin and possessed low in vitro biological activities of 2.5-17%. Crystallization attempts failed. Thus, the introduction of side chains in position A1 distorts the conformation sterically and decreases the biological activity.

Amino Acid Sequence↗
PubMed1975

[Partial synthesis and properties of des-A1-glycine-insulin (author's transl)].

Des-Gly-A-chain-tetra-S-sulphonate was prepared by Edman degradation following two different routes. A) Via complete reaction of A-chain from bovine insulin with 150 equivalents of phenylisothiocyanate in pyridine/water and trifluoroacetic acid cleavage of the resulting phenylthiocarbamoyl A-chain. B) Via reaction of bovine insulin with about 20 equivalents of phenylisothiocyanate until a substitution degree of 2.3-2.5 was reached, trifluoroacetic acid cleavage of the crude derivatives and oxidative sulphitolysis of the resulting desaminoacyl insulins. Preparative electrophoresis (pH 2) or ion exchange chromatography using DEAE-Sephadex gave des-Gly-A-chain in a yield of 60-65% of theory according to method B, containing less than 1% of glycine. Des-GlyA1-insulin was prepared by combination with 0.67 equivalents of B-chain-bis-S-sulphonate and isolated in yields of 5-13%, based on B-chain, after gel filtration (pH 8) and ion exchange chromatography (CM-cellulose, pH 3-2). The electrophoretically (pH 2 and 8.6) homogeneous analogue did not crystallize in the presence of zinc ions. Its blood sugar lowering potency is 10-25%, its in vitro insulin activity (fat cell assay) only 1-2%. The immunoreactivity against anti-insulin sera in different test systems is markedly reduced. There are clear differences between the CD-spectra of des-Gly-insulin and insulin, indicating a loss of ordered secondary structure. From the results it is concluded that structure-stabilizing non covalent bonds are abolished by the removal of the invariant A1-glycine. This leads to conformational alterations which cause the far-going inactivation of the molecule.

Amino Acid Sequence↗