Comparison of LC-MS-MS and GC-MS Analysis of Benzodiazepine Compounds Included in the Drug Demand Reduction Urinalysis Program.

Liquid chromatography-tandem mass spectrometry (LC-MS-MS) offers specific advantages over gas chromatography-mass spectrometry (GC-MS) such as the ability to identify and measure a broader range of compounds with minimal sample preparation. Comparative analysis of LC-MS-MS versus GC-MS was performed for urinalysis detection of five benzodiazepine compounds currently part of the Department of Defense (DoD) Drug Demand Reduction Program (DDRP) testing panel; alpha-hydroxyalprazolam, oxazepam, lorazepam, nordiazepam and temazepam. In the analyses of internally prepared control urine samples at concentrations around the DDRP administrative decision point for benzodiazepines (100 ng/mL), both technologies produced comparable results with average accuracies between 99.7 and 107.3% and average coefficients of variation (%CV) <9%. Analysis of service member specimens that screened positive for benzodiazepines using both technologies produced comparable results for all analytes. Different degrees of matrix effect were observed for all analytes in the LC-MS-MS analysis. However, the effects were controlled by using deuterated internal standards (ISTDs). Additionally, there was a 39% increase in nordiazepam mean concentration analyzed by LC-MS-MS due to suppression of the ISTD ion by the flurazepam metabolite 2-hydroxyethylflurazepam. The ease and speed of sample extraction, the broader range of compounds that can be analyzed and shorter run time make the LC-MS-MS technology a suitable and expedient alternative confirmation technology for benzodiazepine testing.

Structural basis of hAT transposon end recognition by Hermes, an octameric DNA transposase from Musca domestica.

Hermes is a member of the hAT transposon superfamily that has active representatives, including McClintock's archetypal Ac mobile genetic element, in many eukaryotic species. The crystal structure of the Hermes transposase-DNA complex reveals that Hermes forms an octameric ring organized as a tetramer of dimers. Although isolated dimers are active in vitro for all the chemical steps of transposition, only octamers are active in vivo. The octamer can provide not only multiple specific DNA-binding domains to recognize repeated subterminal sequences within the transposon ends, which are important for activity, but also multiple nonspecific DNA binding surfaces for target capture. The unusual assembly explains the basis of bipartite DNA recognition at hAT transposon ends, provides a rationale for transposon end asymmetry, and suggests how the avidity provided by multiple sites of interaction could allow a transposase to locate its transposon ends amidst a sea of chromosomal DNA.