Arylstibonic acids: novel inhibitors and activators of human topoisomerase IB.

Human topoisomerase IB (hTopo) forms a covalent phosphotyrosyl linkage with the DNA backbone, and controls genomic DNA topology by relaxing DNA supercoils during the processes of DNA replication, transcription, chromosome condensation and decondensation. The essential role of hTopo in these processes has made it a preeminent anticancer drug target. We have screened a small library of arylstibonic acids for their effects on plasmid supercoil relaxation catalyzed by hTopo.

Cross-polarization schemes for peptide samples oriented in hydrated phospholipid bilayers.

Continuous-wave, ramped amplitude, and frequency modulated cross-polarization schemes (abbreviated as CWCP, RACP, and FMCP, respectively) are evaluated for static samples in anisotropic phases, such as peptides oriented in lipid environments. It is shown experimentally that both RACP and FMCP give rise to 20% higher polarized signal intensity in comparison to CWCP. The CP matching bandwidths for CWCP and RACP are about the same.

The effect of Hartmann-Hahn mismatching on polarization inversion spin exchange at the magic angle.

The effect of the Hartmann-Hahn mismatch delta = omega(eff)-omega(1S) during polarization inversion spin exchange at the magic angle (PISEMA) has been investigated, where omega(eff) and omega(1S) represent the amplitudes of the 1H effective spin-locking field at the magic angle and the 15N RF spin-locking field, respectively. During the PISEMA evolution period, the exact Hartmann-Hahn match condition (i.e.