PubMed · 4784532
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V Neuhoff. 1973. Capillary centrifugation.. https://doi.org/10.1007/978-3-642-80761-9_5
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Various site-specific recombination enzymes produce different types of knots or catenanes while acting on circular DNA in vitro and in vivo. By analysing the types of knots or links produced, it is possible to reconstruct the order of events during the reaction and to deduce the molecular "architecture" of the complexes that different enzymes form with DNA. Until recently it was necessary to use laborious electron microscopy methods to identify the types of knots or catenanes that migrate in different bands on the agarose gels used to analyse the products of the reaction. We reported recently that electrophoretic migration of different knots and catenanes formed on the same size DNA molecules is simply related to the average crossing number of the ideal representations of the corresponding knots and catenanes. Here we explain this relation by demonstrating that the expected sedimentation coefficient of randomly fluctuating knotted or catenated DNA molecules in solution shows approximately linear correlation with the average crossing number of ideal configurations of the corresponding knots or catenanes.
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OBJECTIVE: To compare the effectiveness of three methods of sperm preparation for IUI during superovulation of infertile women. DESIGN: Randomized assignment of one of three sperm preparation methods. SETTING: University infertility practice. PATIENT(S): Infertile couples undergoing superovulation and IUI. INTERVENTION(S): The method of preparation of sperm for IUI during superovulation was assigned randomly to double centrifugation, multiple-tube swim-up, or Percoll density gradient. MAIN OUTCOME MEASURE(S): Total number and percent recovery of motile sperm, percent of recovered sperm with normal morphology, and cycle fecundity. RESULT(S): No method of sperm preparation provided better cycle fecundity than the others despite differences in sperm recovery. CONCLUSION(S): Double centrifugation, multiple-tube swim-up, and Percoll density gradient sperm preparation for IUI yield similar cycle fecundity rates.