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Frank Kramer

Publications and source records attributed to Frank Kramer.

7 recordsLinked to original sources
PubMed2005

Optimal experiments for maximizing coherence transfer between coupled spins.

In spite of great advances in the theory and applications of magnetic resonance in the past 50 years, some basic questions in spin physics have not yet been answered. In the absence of relaxation losses, what is the maximum amount of coherence that can be transferred between coupled spins under general coupling tensors in a given time and how can this be realized experimentally? Since transfer of coherence between spins forms the basis for multidimensional experiments in NMR spectroscopy, the answers to these questions are of both practical and theoretical interest. Computing the physical limits of coherence transfer involves characterizing all unitary evolutions that can be synthesized in a given time. Here we derive these limits and show how they can be achieved experimentally.

Journal Article↗
PubMed2004

Protein kinase C pathway is involved in transcriptional regulation of C-reactive protein synthesis in human hepatocytes.

OBJECTIVE: C-reactive protein (CRP) is the prototype acute phase protein and a cardiovascular risk factor. Interleukin-1beta (IL-1beta) and IL-6 stimulate CRP synthesis in hepatocytes. We searched for additional pathways regulating CRP expression. METHODS AND RESULTS: Primary human hepatocytes (PHHs) were treated with IL-1beta, IL-6, and protein kinase C (PKC) activator phorbol 12,13-dibutyrate (PDBu). CRP was analyzed by quantitative RT-PCR and ELISA. PDBu significantly induced CRP transcription by 21.0+/-9.24-fold and protein release by 2.9+/-0.5-fold. Transcriptional regulation was studied in detail in hepatoma G2 (HepG2) cells stably transfected with the 1-kb CRP promoter (HepG2-ABEK14 cells). In these cells, PDBu significantly induced CRP transcription by 5.39+/-0.66-fold. Competitive inhibition with bisindolylmaleimide derivative LY333531 abolished PDBu-mediated promoter activation. Competitive inhibition with IkappaB kinase inhibitor I229 also inhibited PDBu effects. Importantly, IL-8 significantly induced CRP release in PHHs by 58.675+/-19.1-fold, which was blockable by LY333531. CONCLUSIONS: This study describes a novel PKC-dependent transcriptional regulation of CRP gene expression, which, in analogy to the classical IL-1beta and IL-6 pathways, is operational in hepatocytes only. It also identifies IL-8 as a potential physiological PKC activator. HepG2-ABEK14 cells may be useful for high throughput screening to identify inhibitors of CRP synthesis for the prevention of cardiovascular disease.

Aorta↗
PubMed2004

Homonuclear Hartmann-Hahn transfer with reduced relaxation losses by use of the MOCCA-XY16 multiple pulse sequence.

Homonuclear Hartmann-Hahn transfer is one of the most important building blocks in modern high-resolution NMR. It constitutes a very efficient transfer element for the assignment of proteins, nucleic acids, and oligosaccharides. Nevertheless, in macromolecules exceeding approximately 10 kDa TOCSY-experiments can show decreasing sensitivity due to fast transverse relaxation processes that are active during the mixing periods. In this article we propose the MOCCA-XY16 multiple pulse sequence, originally developed for efficient TOCSY transfer through residual dipolar couplings, as a homonuclear Hartmann-Hahn sequence with improved relaxation properties. A theoretical analysis of the coherence transfer via scalar couplings and its relaxation behavior as well as experimental transfer curves for MOCCA-XY16 relative to the well-characterized DIPSI-2 multiple pulse sequence are given.

Algorithms↗
PubMed2004

Clean TOCSY transfer through residual dipolar couplings.

The transfer efficiency of cross-relaxation compensated (Clean) TOCSY sequences is analyzed for applications to residual dipolar couplings. Surprisingly most conventional Clean TOCSY sequences are very inefficient for dipolar transfer. It is shown theoretically, that this is a general property of all phase-alternating mixing sequences, i.e., for such sequences the suppression of cross-relaxation excludes dipolar transfer in the spin-diffusion limit. A new family of clean dipolar TOCSY sequences is derived which provides excellent transfer efficiencies for a broad range of offset frequencies.

Journal Article↗
PubMed2002

Efficiency of homonuclear Hartmann-Hahn and COSY-type mixing sequences in the presence of scalar and residual dipolar couplings.

In the presence of scalar (J) and residual dipolar (D) couplings, the transfer efficiency of homonuclear Hartmann-Hahn and COSY-type mixing depends on the ratio D/J and on the mixing sequence. This dependence is analyzed theoretically and the results are confirmed experimentally. At least two different mixing sequences are required to yield good transfer efficiencies for all ratios D/J. In contrast to COSY-type experiments, homonuclear Hartmann-Hahn sequences can provide efficient transfer even if the sum of D and J is zero, i.e., if the coupling vanishes in the weak coupling limit.

Journal Article↗
PubMed2002

Determination of residual dipolar couplings in homonuclear MOCCA-SIAM experiments.

In solutions with partial molecular alignment, anisotropic magnetic interactions such as the chemical shift anisotropy, the electric quadrupole interaction, and the magnetic dipole-dipole interaction are no longer averaged out to zero in contrast to isotropic solutions. The resulting residual anisotropic magnetic interactions are increasingly used in biological NMR studies for the determination of 3D structures of proteins and other biomolecules. In the present paper we propose a new approach allowing the measurement of residual HN-H(alpha) dipolar couplings of non-isotope enriched proteins based on the application of the MOCCA-SIAM experiment. This experiment allows the measurement of homonuclear coupling constants with an accuracy of ca. +/- 0.2 Hz and is therefore particularly well suited to determine residual dipolar couplings at relatively low degrees of molecular orientation. The agreement between experimentally determined residual HN-H(alpha) couplings and calculated values is demonstrated for BPTI.

Animals↗