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Biomedical subjects

H F Fan

Publications and source records attributed to H F Fan.

5 recordsLinked to original sources
PubMed2001

Electron crystallographic image-processing investigation and superstructure determination for (Pb0.5Sr0.3Cu0.2)Sr2(Ca0.6Sr0.4)Cu2Oy.

An electron crystallographic image-processing technique based on the combination of high-resolution electron microscopy and electron diffraction has been developed to investigate the commensurate structural modulation in the high-Tc superconductor (Pb0.5Sr0.3Cu0.2)Sr2(Ca0.6Sr0.4)Cu2Oy. After symmetry averaging, a structure image was obtained by image deconvolution at the resolution limited by that of the electron microscope. Then phase extension was employed to enhance the image resolution up to about 1.25 A by means of the electron diffraction data corrected with an empirical method. In the final projected potential map, the occupational and/or positional modulation is clearly observed for all atoms, including oxygen. The key points of determining superstructures by the technique are studied and discussed.

Journal Article↗
PubMed2001

Direct-method-aided phasing of MAD data.

The direct methods of breaking the phase ambiguity intrinsic in one-wavelength anomalous scattering (OAS) data and MAD phasing are powerful methods in their own rights. In a different context, in addition to their success in phasing OAS data, direct methods can also be useful in the treatment of MAD data. The idea has been tested with the MAD data at 2.5 A resolution from the protein human adenosine kinase [Mathews et al. (1998), Biochemistry, 37, 15607--15620]. The results showed that the incorporation of direct methods in MAD phasing led to a significant improvement of phases over those obtained from the conventional MAD phasing method alone, as indicated by improved map correlation coefficients (with the existing model), reduced phase errors by 4.5 degrees and improved map connectivity.

Adenosine Kinase↗
PubMed1999

Combining direct methods with isomorphous replacement or anomalous scattering data. VIII. Phasing experimental SIR data with the replacing atoms in a centrosymmetric arrangement.

A multisolution direct method has been proposed to resolve the phase ambiguity intrinsic in single isomorphous replacement data of proteins with the replacing atoms in a centrosymmetric arrangement. The phase ambiguity of each reflection is in fact a 'sign ambiguity' of the phase difference between the phase of the native protein and that of the replacing atoms, i.e. +/- |Deltatheta| = theta - theta'. The P+ probability formula can be used to derive the signs. The multisolution phasing procedure is initiated using random starting values of P+. A cluster analysis is used instead of figures of merit to find the correct solution. The direct-method phases can be further improved by density-modification techniques. The method was tested with the experimental SIR data at 2 A resolution from a known protein aPP; satisfactory results were obtained.

Animals↗
PubMed1986

Loss of propranolol during ultrafiltration in plasma protein binding studies.

A commercial ultrafiltration device was examined for propranolol plasma protein binding studies. A nonspecific loss of free drug resulted in a low recovery in the ultrafiltrate. Use of a rinse filtrate did not completely compensate for this loss. Use of different centrifugal forces indicated the loss was not due to significant membrane rejection of drug. Equilibrating the device with sample for four hours slightly improved the recovery while use of a higher ionic strength buffer had no effect. Propranolol was bound by the membrane, but there was a larger, continuous loss to the o-ring. Results with an alternate commercial device were also unsatisfactory.

Blood Proteins↗