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Biomedical subjects

R W Webster

Publications and source records attributed to R W Webster.

9 recordsLinked to original sources
PubMed2001

A virtual reality surgical trainer for navigation in laparoscopic surgery.

A virtual reality trainer was designed to familiarize students and surgeons with surgical navigation using an angled laparoscopic lens and camera system. Previous laparoscopic trainers have been devoted to task or procedure training. Our system is exclusively devoted to laparoscope manipulation and navigation. Laparoscopic experts scored better than novices in this system suggesting construct validity. The trainer received favorable subjective ratings. This simulator may provide for improved navigation in the operating room and become a useful tool for residents and practicing surgeons.

Computer Simulation↗
PubMed2001

A prototype haptic suturing simulator.

A new haptic simulation designed to teach basic suturing for simple wound closure is described. Needle holders are attached to the haptic device as the graphics of the needle holders, needle, sutures and virtual skin are displayed and updated in real time. The simulator incorporates several interesting components such as real-time modeling of deformable skin, tissue and suture material and real-time recording of state of activity during the task using a finite state model.

Computer Graphics↗
PubMed1979

In vivo inhibitors of Escherichia coli phenylalanyl-tRNA synthetase.

N-Benzyl-D-amphetamine is a potent in vitro and in vivo inhibitor of phenylalanyl-tRNA synthetase of Escherichia coli. The concentration of this inhibitor necessary for the in vivo inhibition is approximately 100-fold greater than that necessary for inhibition of the purified enzyme. Treatment of rel+ strains of E. coli with the inhibitor results in a decreased percentage of tRNA Phe which is charged, guanosine tetraphosphate formation, cessation of RNA synthesis, and growth arrest. Evidence is presented which demonstrates that the primary and perhaps sole mode of action of N-benzyl-D-amphetamine is inhibition of phenylalanyl-tRNA synthetase.

Amino Acyl-tRNA Synthetases↗
PubMed1976

Phenylalanyl transfer ribonucleic acid synthetase from rat liver. Analysis of phenylalanine and adenosine 5'-triphosphate binding sites and comparison to the enzyme from Escherichia coli.

Inhibition of the ATP--PPi exchange reaction catalyzed by rat liver phenylalanyl-tRNA synthetase by structural analogues of L-phenylalanine and ATP has been examined and compared with data reported for the enzyme from E. coli. The phenylalanine binding sites are similar in the following characteristics. (1) The region that complexes the phenyl ring shows a strict requirement for the unsubstituted phenyl ring altough the rat liver enzyme is more tolerant in this respect. (2) The protonated amino group of phenylalanine is required for binding. (3) The region neighboring the binding site for the carboxylate of phenylalanine is diffusely hydrophobic. Unlike effects of these modifications on interaction with the E. coli enzyme, substitution of the carboxylate by hydrophobic groups leads to large losses in affinity for the rat liver enzyme. Although both enzymes bind D-phenylalanine very poorly, their relative affinities for the D isomers of phenylalanine analogues vary greatly. The most dramatic difference is observed with N-benzyl-D-amphetamine, which binds 24 000-fold tighter to E. coli phenylalanyl-tRNA synthetase than the rat liver enzyme. The affinity of rat liver phenylalanyl-tRNA synthetase for naturally occurring adenine compounds is similar to that of the E. coli enzyme, suggesting that the binding of ATP occurs via similar interactions. Adenine provides a major protion of the free energy of binding of ATP. The remainder may be viewed as the sum of detrimental interactions with the phosphate groups of ATP and a favorable contribution by the ribose moiety.

Adenosine Triphosphate↗
PubMed1975

The role of polyamines in the aminoacyl transfer ribonucleic acid synthetase reactions. Demonstration of the requirement for magnesium ion and a secondary stimulatory effect of spermine.

Spermine and related polyamines have been reported to substitute for Mg2+ in the aminoacylation of tRNA catalyzed by aminoacyl-tRNA synthetases, but not in the ATP-PP-i exchange reaction. Such observations have led some workers to propose that these reactions proceed via a concerted mechanism rather than the usual two-step mechanism involving an aminoacyladenylate intermediate. In an attempt to elucidate the mechanism of the spermine effect on acylation and exchange, both reactions were re-examined using isoleucyl-tRNA synthetase from Escherichia coli. In the absence of added Mg2+ untreated tRNA was acylated in the presence of spermine, but tRNA from which Mg2+ had been scrupulously removed was not. ATP-PP-i exchange was not observed when spermine was used in place of Mg2+; however, if tRNA possessing sequestered Mg2+ was added, the exchange reaction was observed. These data suggest that a primary effect of spermine is to displace bound Mg2+ from tRNA in quantities sufficient to promote both the ATP-PP-i exchange and esterification of tRNA. The previously reported stimulatory effects of polyamines on these reactions are believed to be artifacts due to Mg2+ contamination of tRNA. Providing trace levels of Mg2+ are present, spermine exerts a secondary stimulation of the rate of aminoacylation, the mechanism of which is unknown. The results presented refute arguments that these enzymes proceed by a concerted mechansim and support the intermediacy of aminoacyladenylates.

Adenosine Triphosphate↗