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J N Sanders

Publications and source records attributed to J N Sanders.

4 recordsLinked to original sources
PubMed1998

Effect of metal ion substitutions in concanavalin A on the binding of carbohydrates and on thermal stability.

Isothermal titration calorimetry (ITC) measurements were performed on the binding of alpha methyl-D-mannopyranoside, D-mannopyranose, alpha methyl-D-glucopyranoside, and D-glucopyranose (Glu) to cobalt, nickel, and cadmium substituted concanavalin A (Con A) derivatives at pH = 6.9 and at 25 degrees C. The metal substituted Con A derivatives consisted of Co2+, Ni2+, and Cd2+ substituted for the Mn2+ ion in the S1 site of Con A which is about 12.8 A away from the center of the carbohydrate binding site of Con A. The thermodynamic quantities determined from the ITC measurements were the same for most of the binding reactions indicating that the structure of the binding site in solution is the same for all the Con A derivatives in solution and that the presence of different 2+ metal ions in the S1 site has little effect on the binding reactions. Differential scanning calorimetry scans of solutions of the metal ion derivatives of Con A show that the thermodynamics of the unfolding transition for the cobalt and nickel substituted derivatives are the same as for Con A: they dissociate from tetramers into monomers as they unfold around 85 degrees C. The cadmium substituted Con A derivative, however, exhibits an additional transition around 93 degrees C which also appears following the addition of Cd2+ to the Con A solutions. This transition results from the unfolding of a species of Con A with Cd2+ substituted into a third binding site at the monomeric interface of the Con A tetramer. The higher stability of this species is not only exemplified by the higher thermal transition temperature but also by the lack of dissociation as it unfolds. Cd2+ is released from the S3 site upon decreasing the pH from 6.9 to 6.4. ITC measurements on the binding reaction of Cd2+ to Con A show that the binding enthalpy is 40.2 +/- 0.4 kJ mol-1 at 23.4 +/- 0.2 degrees C and the binding reaction exhibits a large heat capacity change of 1.43 +/- 0.41 kJ mol-1 K-1.

Binding Sites↗
PubMed1985

Detector for dual-energy digital radiography.

A detection scheme is described that allows one to accomplish dual-energy scanned projection digital radiography without switching the x-ray tube voltage. The method employs a high/low atomic number detector sandwich that simultaneously separates the x-ray beam transmitted by the patient into low and high energy components. To test the method, the response of a scanning linear array of energy-sensitive detectors was simulated, and bone and soft tissue images of an anthropomorphic chest phantom were obtained at 140 kVp. These were compared with similar images obtained by switching the x-ray tube voltage from 80 kVp to a heavily filtered 140 kVp. For comparable entrance skin exposures, the dual-energy detector images required a lower tube load and resulted in higher noise levels. The latter is attributable to the fact that the separation in energy between the high and low energy components is smaller with the dual-energy detector than with the voltage switching technique, and to misregistration problems associated with the simulation methodology. A detector design is also discussed that would result in improved energy separation and lower noise levels. In view of this possibility and the tube loading advantage, the method looks promising for digital scanned projection radiography.

Humans↗
PubMedDate not supplied

A laser-based multiformat camera for medical imaging.

The spatial resolution and contrast resolution required of a multiformat camera (MFC) for medical imaging are discussed. A typical cathode-ray tube (CRT) MFC and a prototype laser MFC are compared based on the following measured quantities: line spread function and associated contrast transfer function, noise characteristics, intensity transfer function (dynamic range), large-area contrast, and film irradiance. The laser MFC is found to provide significantly better performance than the CRT MFC in all of these areas.

Fourier Analysis↗