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P Spear

Publications and source records attributed to P Spear.

7 recordsLinked to original sources
PubMed2004

Advanced electronics for the CTF MEG system.

Development of the CTF MEG system has been advanced with the introduction of a computer processing cluster between the data acquisition electronics and the host computer. The advent of fast processors, memory, and network interfaces has made this innovation feasible for large data streams at high sampling rates. We have implemented tasks including anti-alias filter, sample rate decimation, higher gradient balancing, crosstalk correction, and optional filters with a cluster consisting of 4 dual Intel Xeon processors operating on up to 275 channel MEG systems at 12 kHz sample rate. The architecture is expandable with additional processors to implement advanced processing tasks which may include e.g., continuous head localization/motion correction, optional display filters, coherence calculations, or real time synthetic channels (via beamformer). We also describe an electronics configuration upgrade to provide operator console access to the peripheral interface features such as analog signal and trigger I/O. This allows remote location of the acoustically noisy electronics cabinet and fitting of the cabinet with doors for improved EMI shielding. Finally, we present the latest performance results available for the CTF 275 channel MEG system including an unshielded SEF (median nerve electrical stimulation) measurement enhanced by application of an adaptive beamformer technique (SAM) which allows recognition of the nominal 20-ms response in the unaveraged signal.

Cluster Analysis↗
PubMed1990

Specificity and efficiency of rho-factor helicase activity depends on magnesium concentration and energy coupling to NTP hydrolysis.

The RNA-DNA helicase activity of Escherichia coli transcription termination factor rho can be significantly enhanced at lower potassium chloride and magnesium acetate concentrations than previously used. Decreasing the potassium chloride concentration from 150 to 50 mM increases the rate of release at least 4-fold, while at lower magnesium concentrations less ATP is required for maximal duplex disruption. For all concentrations tested (between 0.1 and 5 mM), the optimal magnesium and ATP concentrations are interdependent; a roughly equimolar ratio gives the maximal rate of RNA release, although peak height and breadth vary. Surprisingly, rho behaves differently with an RNA-RNA duplex, which cannot be efficiently disrupted at magnesium concentrations below 1 mM. Above 2.0 mM, release does occur efficiently suggesting that Mg2+ promotes some structural transition in the RNA-RNA helix to a rho-susceptible conformation. In addition to Mg2+, helicase activity requires hydrolysis of nucleoside triphosphates, but for all four standard NTPs the rates of NTP hydrolysis do not correlate uniformly with the rates of RNA release. Based on the ratio of the rate of RNA release to the rate of NTP hydrolysis, rho utilizes ATP most efficiently. The 2-4-fold weaker coupling of hydrolysis to duplex disruption for the other three NTPs demonstrates that NTP utilization is not, on its own, sufficient for efficient helicase activity. The less efficient coupling with GTP, CTP, and UTP correlates with conformational differences in the protein complex as probed by mild trypsin digestion. The implications of our findings for substrate specificity and energy coupling in the helicase reaction are discussed.

Adenosine Triphosphatases↗
PubMed1988

Site-directed alterations in the ATP-binding domain of rho protein affect its activities as a termination factor.

We have utilized oligonucleotide site-directed mutagenesis to test our prediction that Escherichia coli rho factor has an ATP-binding domain separate from its RNA-binding domain and similar to that of adenylate kinase. Single amino acid substitutions were generated in regions thought to be within the active site and catalytically important for the ATPase activity, changing lysine 181 and/or lysine 184 to glutamine, and aspartate 265 to valine and asparagine. The altered proteins were purified and characterized in vitro for RNA- and ATP-binding ability, ATPase activity, helicase activity, and ability to catalyze transcription termination. Our results indicate that 1) these amino acid alterations in the proposed ATP-binding domain do not interfere with RNA binding; 2) substitution of lysine 184 by glutamine actually improves the ATPase and related activities while the same substitution at lysine 181 reduces but does not eliminate activity; 3) the double mutation changing both lysine 181 and lysine 184 to glutamine eliminates ATPase activity; and 4) the aspartate at 265 is also required for ATP hydrolysis but not for ATP binding. These results are consistent with our proposal that the general tertiary structure of rho's ATP-binding domain is similar to that of adenylate kinase.

Adenosine Triphosphatases↗
PubMedDate not supplied

Evaluation of poly(styrene-4-sulfonate) as a preventive agent for conception and sexually transmitted diseases.

A commercial preparation of a sodium polystyrene sulfonate (designated as N-PSS; its molecular weight is 500000 daltons) was tested as an inhibitor of sperm function and as a preventive agent for conception and the transmission of sexually transmitted diseases. The polymer is an irreversible inhibitor of hyaluronidase and acrosin; its IC50 values are 5.7 microg/mL and 0.5 microg/mL, for hyaluronidase and acrosin, respectively. N-PSS is also a stimulus of human sperm acrosomal loss. It produces maximal acrosomal loss at 2.5 microg/mL. Contraception in rabbits is nearly complete when rabbit spermatozoa are pretreated with 0.5 mg/mL of N-PSS before artificial insemination; however, N-PSS does not immobilize spermatozoa at concentrations as high as 50 mg/mL. N-PSS has broad spectrum antiviral and antibacterial activities. Infection by human immunodeficiency virus and herpes simplex virus are inhibited by N-PSS; 3-log reductions are produced by 7 microg/mL and 3 microg/mL, respectively. N-PSS is active against Chlamydia trachomatis and Neisseria gonorrhoeae. At 1 mg/mL, N-PSS inhibits chlamydial infectivity by more than 90%. N-PSS produces a 3-log reduction in gonococcal growth at 15 microg/mL. In contrast, N-PSS (5 mg/mL) does not affect the growth of Lactobacillus (normal component of the vaginal flora). N-PSS can be classified as a noncytotoxic contraceptive antimicrobial agent. These properties justify bringing a polystyrene sulfonate into clinical trials for its evaluation as a preventive agent for conception and several sexually transmitted diseases.

Animals↗