The electrophoretic mobility of two small DNA plasmids, pUC19 and Litmus 28, linerarized by digestion with a variety of single-cut restriction enzymes, has been studied. The permuted sequence isomers migrate with identical mobilities in agarose gels, as expected, but exhibit different mobilities in large-pore polyacrylamide gels, suggesting that the parent plasmids contain sequence-specific sites of curvature and/or anisotropic flexibility. Both plasmids contain apparent bend centers near their origin(s) of replication; pUC19 also has a major apparent bend center near the promoter of the ampicillin resistance gene. These apparent bend centers are observed under a variety of experimental conditions, suggesting that they correspond to sites of stable curvature in the parent plasmids. Both plasmids also contain minor bend centers that are observed under a sub-set of electrophoretic conditions and disappear when divalent cations are added to the solution, suggesting that these apparent bend centers may correspond to localized regions of variable flexibility.

The electrophoresis of small DNA fragments has been measured in dilute agarose and polyacrylamide gels cast and run in Tris-acetate-EDTA (TAE) and Tris-borate-EDTA (TBE) buffers. Ferguson plots were constructed to extrapolate the mobilities to zero gel concentration and estimate the free solution mobility of DNA. In polyacrylamide gels, in both TAE and TBE buffers, the extrapolated mobilities at zero gel concentration increased gradually with decreasing DNA molecular weight, went through a maximum at approximately 60 bp, and then decreased again. The increase in the extrapolated mobilities with decreasing molecular weight observed for DNA fragments > or = 60 bp can be attributed to transient interactions between the migrating DNA molecules and the polyacrylamide gel fibers. If such interactions are eliminated by extrapolating the mobilities to both zero gel concentration and zero DNA molecular weight, the apparent free solution mobility of DNA is found to be 3.1 x 10(-4) cm2 V(-1) s(-1) in TAE buffer and 4.2 x 10(-4) cm2 V(-1) s(-1) in TBE buffer at 20 degrees C, reasonably close to the actual free solution mobilities measured in the same two buffers by capillary electrophoresis (N. C. Stellwagen et al., Biopolymers 1997, 42, 687-703). The significantly larger electrophoretic mobility observed in TBE buffer is most likely due to the formation of nonspecific, highly charged deoxyribose-borate complexes in this buffer medium. For DNA molecules < or = 60 bp in size, the decrease in the extrapolated mobilities with decreasing molecular weight parallels the decrease in their free solution mobilities observed by capillary electrophoresis. In agarose gels, the extrapolated mobilities of small DNA molecules at zero gel concentration appear to be independent of molecular weight. The apparent free solution mobilities are found to be (3.0 +/- 0.1) x 10(-4) cm2 V(-1) s(-1) in TAE buffer and (3.2 +/- 0.1) x 10(-4) cm2 V(-1) s(-1) in TBE buffer. The very similar mobilities observed in the two buffer media suggest that the borate ions in TBE buffer primarily form complexes with the galactose residues in the agarose gel fibers, rather than with the migrating DNA molecules, because of mass action effects. The formation of borate-agarose complexes, increasing the net negative charge of the agarose gel fibers, appears to be responsible for the markedly increased electroendosmotic flow observed in agarose gels cast and run in TBE buffer (N. C. Stellwagen, Electrophoresis 1992, 13, 601-603).

Within the last 10 years, the incorporation of off-pump coronary artery bypass grafting (OPCAB) into many surgical practices has grown. OPCAB requires the surgeon to operate on a beating heart, and it is generally accepted that OPCAB procedures are more technically demanding. Concerns of possible incomplete revascularizations and decreased graft patency have been noted in the literature. The objective of this study was to evaluate and compare on-pump and off-pump intraoperative coronary artery bypass graft (CABG) flow parameters. Intraoperative flow studies conducted with the Butterfly (Medi-Stim Norge AS, Oslo, Norway) flow meter were analyzed retrospectively on 74 patients. Comparisons were completed between patient groups having had their revascularizations performed on or off cardiopulmonary bypass. Our study revealed significant differences in the mean flow rate through saphenous vein grafts (SVG) to the obtuse marginal artery (OM; p = .014), to the diagonal artery (Diag; p = .003), to the right coronary artery (RCA; p = .001), and to the posterior descending artery (PDA; p = .001). Total blood product use showed significantly increased use of both platelets (PLTs) and cryoprecipitate (Cryo) in the on-pump group (p = .027 and .012, respectively). No differences were found for transfusions of red blood cells (RBCs) or fresh frozen plasma (FFP). Additional findings showed a significantly decreased median length of stay (LOS) for the off-pump group. The on-pump patients had a median hospital stay of 7 days (range, 4–24 days), whereas the off-pump patients had a median stay of 6 days (range, 3–22 days; p = .049). Although we were able to show some significance in the mean flow data supporting increased graft flow with the on-pump technique, we were not able to show an overall increase in all recorded flow characteristics to support one method over another.