Biomedical subjects

Axel Schulz

Publications and source records attributed to Axel Schulz.

27 records · Page 2Linked to original sources

PubMed2004

Effects of tourniquet-induced ischemia on the release of proopiomelanocortin derivatives determined in peripheral blood plasma.

Proopiomelanocortin (POMC) is expressed in pituitary, central nervous system, and in a few peripheral tissues. This study addresses the hypothesis that metabolic stressors, such as acidosis, may induce the release of POMC derivatives into the cardiovascular system not only from the pituitary but also from other sites of POMC expression. In our study, we investigated the liberation of POMC derivatives from peripheral tissues under a state of acidosis achieved by tourniquet-induced ischemia, alteration of lactate concentration, and base excess. In eight patients undergoing knee arthroplasty under spinal anesthesia, catheters were inserted into the femoral vein proximally to thigh tourniquet location. Blood was drawn from these catheters 5 min before and 40 s, 5 min, and 10 min after tourniquet deflation to measure plasma concentrations of N-acetyl-beta-endorphin immunoreactive material (IRM), beta-endorphin IRM, authentic beta-endorphin, adrenocorticotropin, lactate, pH, and base excess. In five of eight patients, we found a significant increase of beta-endorphin IRM levels 40 s after tourniquet deflation compared with predeflation levels; 5 and 10 min after tourniquet deflation, the beta-endorphin IRM levels were below the detection limit. Thus beta-endorphin IRM was released from ischemic limb tissues into the cardiovascular system. Only a small part of the determined beta-endorphin IRM corresponded to authentic beta-endorphin. Forty seconds after tourniquet deflation, the beta-endorphin IRM concentration correlated with base excess (r < 0.71; P < 0.05); no significant correlations were found with pH or lactate levels. Thus it was shown here for the first time that ischemic stress may induce the release of beta-endorphin IRM from nonpituitary tissues.

Aged↗

PubMed2004

Recombinant production, purification and biochemical characterization of domain 6 of LEKTI: a temporary Kazal-type-related serine proteinase inhibitor.

Lympho-epithelial Kazal-type-related inhibitor (LEKTI) is a 15-domain serine proteinase inhibitor which is of pathophysiological relevance for skin diseases and atopy. Domains 2 and 15 of LEKTI contain six cysteine residues and match the Kazal-type inhibitor motif almost exactly. The other 13 domains seem to be Kazal-type derived but lack the cysteines in positions 3 and 6 usually conserved within this family of inhibitors. Here, we report the recombinant production and comprehensive biochemical characterization of the 7.7 kDa LEKTI domain 6 (LD-6). Testing a selected number of different serine proteinases, we show that both native and recombinant LD-6 exhibit a significant but temporary inhibitory activity on trypsin. Furthermore, the relation of LEKTI domain 6 to Kazal-type inhibitors is confirmed by determining its disulfide bond pattern (1-4/2-3) and its P(1) site located after the second Cys residue of LD-6. The established strategy for the recombinant production of LEKTI domain 6 will enable further investigation of its mode of action and its physiological role.

Amino Acid Sequence↗

PubMed2004

Stability and cleavage conditions of (2-furyl)-L-alanine-containing peptides.

The furyl group of (2-furyl)-L-alanine-containing peptides obtained from Fmoc solid-phase synthesis is partially degraded to several by-products during the final TFA-mediated deprotection in the presence of cation scavengers such as ethanedithiol and propanedithiol. The major by-product corresponds to a bis-dithioacetale formed after acidic hydrolysis of the furyl group. We examined several cleavage conditions and found that cleavage cocktails containing water and triisopropylsilane or 3,6-dioxa-1,8-octanedithiol (DODT) in trifluoroacetic acid are sufficient to minimize the side reaction.

Alanine↗

PubMed2003

Electronic effects in 12-metallacrown-3 complexes. A theoretical and experimental study.

The Mulliken charges of the 12-metallacrown-3 complex [(C(6)H(6))Ru(C(5)H(3)NO(2))](3) were determined by a single point analysis at the HF level. For comparison, a Mulliken population analysis was carried out for the organic analogue 12-crown-3. The partial negative charges on the O-donor atoms of the metallamacrocycle were found to be larger than those on the O-donor atoms of 12-crown-3. The 12-metallacrown-3 complex [(cymene)Ru(C(5)H(2)ClNO(2))](3) with chloro-substituents in position 5 of the pyridonate ligand was synthesized to determine the effect of electron withdrawing groups on the structure and the host-guest properties of the receptor. The chloro-substituents were found to have only a small influence on the structures, but they reduce the binding affinity for LiCl and NaCl by approximately 2 orders of magnitude.

Journal Article↗

PubMed2003

Homologous proteins with different folds: the three-dimensional structures of domains 1 and 6 of the multiple Kazal-type inhibitor LEKTI.

We have determined the solution structures of recombinant domain 1 and native domain 6 of the multi-domain Kazal-type serine proteinase inhibitor LEKTI using multi-dimensional NMR spectroscopy. While two of the 15 potential inhibitory LEKTI domains contain three disulfide bonds typical of Kazal-type inhibitors, the remaining 13 domains have only two of these disulfide bridges. Therefore, they may represent a novel type of serine proteinase inhibitor. The first and the sixth LEKTI domain, which have been isolated from human blood ultrafiltrate, belong to this group. In spite of sharing the same disulfide pattern and a sequence identity of about 35% from the first to the fourth cysteine, the two proteins show different structures in this region. The three-dimensional structure of domain 6 consists of two helices and a beta-hairpin structure, and closely resembles the three-dimensional fold of classical Kazal-type serine proteinase inhibitors including the inhibitory binding loop. Domain 6 has been shown to be an efficient, but non-permanent serine proteinase inhibitor. The backbone geometry of its canonical loop is not as well defined as the remaining structural elements, providing a possible explanation for its non-permanent inhibitory activity. We conclude that domain 6 belongs to a subfamily of classical Kazal-type inhibitors, as the third disulfide bond and a third beta-strand are missing. The three-dimensional structure of domain 1 shows three helices and a beta-hairpin, but the central part of the structure differs remarkably from that of domain 6. The sequence adopting hairpin structure in domain 6 exhibits helical conformation in domain 1, and none of the residues within the putative P3 to P3' stretch features backbone angles that resemble those of the canonical loop of known proteinase inhibitors. No proteinase has been found to be inhibited by domain 1. We conclude that domain 1 adopts a new protein fold and is no canonical serine proteinase inhibitor.

Amino Acid Sequence↗

PubMed2002

Native and recombinant proguanylin feature identical biophysical properties and are monomeric in solution.

Guanylin, an intestinal peptide hormone and endogenous ligand of guanylyl cyclase C, is produced as the corresponding prohormone proguanylin. The mature hormone consists of 15 amino acid residues, representing the COOH-terminal part of the prohormone comprised of 94 amino acid residues. Here we report the recombinant expression and purification of proguanylin with its native disulfide connectivity, as well as the biophysical characterization of the recombinant and native protein. The comparison of recombinant and native proguanylin revealed identical biophysical and structural properties, as deduced from CZE, HPLC, and mass spectrometry, as well as NMR spectroscopy and CD spectroscopy at various temperatures and pH values. Exhaustive analytical ultracentrifugation studies were employed for protein concentrations up to the millimolar range to determine the association state of recombinant as well as native proguanylin, revealing both proteins to be monomeric at the applied solution conditions. As a result, a former identified close proximity between the termini of proguanylin is due to intramolecular interactions.

Amino Acid Sequence↗

PubMed2001

NSCl(2)(-): Thiazyl Dichloride-An Aza Analogue of Thionyl Dichloride A.S. thanks Prof. Dr. T. M. Klapötke (LMU München) for his generous support and Prof. Dr. R. D. Harcourt (Melbourne University) for many helpful discussions. We thank Prof. Dr. W. Schnick and S. Schmidt (LMU München) for carrying out the powder diffraction experiments, Dr. K. Karaghiosoff and Dr. J. Senker (MAS) for carrying out the NMR experiments.

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Journal Article↗

PubMed1997

Theoretical Evidence for Two New Intermediate Xenon Species: Xenon Azide Fluoride, FXe(N(3)), and Xenon Isocyanate Fluoride, FXe(NCO).

The reaction behavior of xenon difluoride, XeF(2), toward HN(3), NaN(3), and NaOCN was investigated in H(2)O, aHF (anhydrous HF), and SO(2)ClF solution. The analysis of the final reaction products (XeF(2) + HN(3) (NaN(3)) in H(2)O --> HF, N(2), N(2)O, Xe; XeF(2) + HN(3) in aHF --> N(2), Xe, N(2)F(2); XeF(2) + HOCN (NaOCN) in H(2)O --> HF, N(2), N(2)O, NH(3), CO(2), Xe) indicated the intermediate formation of FXe(N(3)) and FXe(NCO) and revealed different reaction mechanisms for both compounds. Both intermediates, FXe(N(3)) and FXe(NCO), were studied on the basis of ab initio computations at HF and correlated MP2 levels using a quasirelativistic LANL2DZ pseudopotential for Xe. Both were shown to possess stable minima at HF and MP2 levels (no imaginary frequencies) with the following structural parameters (MP2/LANL2DZ). FXe(N(3)): C(s)(); d(F-Xe) = 2.051, d(Xe-N1) = 2.318, d(N1-N2) = 1.241, d(N2-N3) = 1.180 Å; angle(FXeN1) = 178.1, angle(XeN1N2) = 112.2, angle(N1N2N3) = 174.7 degrees. FXe(NCO): C(s)(); d(F-Xe) = 2.024, d(Xe-N) = 2.206, d(N-C) = 1.194, d(C-N) = 1.231 Å; angle(FXeN) = 178.7, angle(XeNC) = 125.4, angle(NCO) = 174.2 degrees. The experimentally unobserved cyanate isomer, FXe(OCN), was calculated to be higher in energy than the isocyanate isomer FXe(NCO): DeltaE = 19.8 (HF), 18.3 (MP2) kcal mol(-)(1).

Journal Article↗

PubMed1996

Azidotris(trifluoromethyl)germane, (CF(3))(3)GeN(3): Spectroscopic Characterization and Density Functional Computations.

Azidotris(trifluoromethyl)germane, (CF(3))(3)GeN(3), was prepared from activated silver azide and iodotris(trifluoromethyl)germane in a neat reaction or in dichloromethane or toluene solution, respectively. (CF(3))(3)GeN(3) is a colorless, highly volatile liquid (mp ca. -85 degrees C) which was identified from MS data. The new compound was characterized by multinuclear solution NMR ((13)C, (14)N, (19)F) and gas-phase IR spectroscopy. The structure and the vibrational spectrum of (CF(3))(3)GeN(3) were computed employing density functional theory calculations (DFT) at the self-consistent level with the nonlocal exchange functional of Becke (B) and the nonlocal correlation functional of Lee, Yang, and Parr (B-LYP). The results of the DFT calculation and experimentally obtained vibrational spectra are in good agreement. The DFT computation at the correlated level (B-LYP) predicts the vibrational modes reasonably well, and no scaling was required.

Journal Article↗