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Z Tan

Publications and source records attributed to Z Tan.

78 records · Page 5Linked to original sources
PubMed1989

Solution conformation of d-CTCGAGCTCGAG by two-dimensional NMR: conformational heterogeneity at XhoI cleavage site.

Nonexchangeable proton resonances in the 500-MHz NMR spectrum of d-CTCGAGCTCGAG have been assigned by using two-dimensional correlated spectroscopy (COSY) and nuclear Overhauser enhancement spectroscopy (NOESY). 1H-1H coupling constants (J) in the deoxyribose rings have been measured by analyzing intensity and multiplet patterns in the phase-sensitive omega 1-scaled COSY spectra. A modification of the J-resolved technique, called amplitude-modulated J-resolved spectroscopy, has been described and used to increase the accuracy of J measurements. Absorption mode omega 1-scaled NOESY spectra at mixing times in the range 50-200 ms have been analyzed to monitor spin diffusion. A 50-ms spectrum has been used to estimate several interproton distances. The coupling constant and distance data have been used to arrive at sequence-specific sugar geometries and glycosidic torsion angles. The backbone structure has been refined by model building using the FRODO program, employing the sugar geometries and glycosidic torsion angles discussed above. The molecule shows interesting sequence-dependent variations in the structure. The cleavage site of the restriction enzyme XhoI exhibits unique differences in the sugar geometry and backbone torsion angles.

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PubMedDate not supplied

Lateralized cortical perfusion in women with Alzheimer's disease.

OBJECTIVE: To define the pathophysiologic substrate of gender differences in cognition and behavior in Alzheimer's disease (AD). DESIGN: Hemispheric regional cerebral blood flow (rCBF) was studied in a consecutive series of dementia patients using single photon emission computed tomography (SPECT). PARTICIPANTS: Subjects included 300 outpatients who were studied with SPECT as part of a diagnostic evaluation for degenerative dementia or memory disorder. METHOD: Based on qualitative descriptions by a radiologist, subjects were classified as having unilateral left, unilateral right, bilateral, or no perfusion defects. Semiquantitative analysis of SPECT images was also performed using region of interest radionuclide counts normalized to the cerebellum. RESULTS: Among 174 females and 126 males, unilateral left hemisphere defects were found more commonly in women than men (24% vs 10%; chi 2 = 9.4; P = .009). This observation was most significant for the 103 females and 62 males regarded as having probable AD (26% vs 8%; chi 2 = 9.3; P = .01). In a multiple regression model of clinical variables, shorter duration of disease and female gender were significant independent predictors of the unilateral left hemisphere pattern among those with probable AD. Age, family history, education, handedness, and severity of cognitive impairment were not significant contributors. CONCLUSIONS: Women with AD exhibit greater heterogeneity in rCBF than men. Asymmetry in rCBF occurs more often in women. In some cases, this is related to relative preservation of right hemisphere function in women.

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