Biomedical subjects
Publications and source records attributed to Ying Zhang.
The pga gene was amplified by PCR from Bacillus megaterium CA4098, cloned into pKK223-3 vector and expressed in E. coli HB101. The pga sequence was also determined. The deduced amino acids sequence was compared with those of PGAs from other bacteria and showed that they were similar, especially the active sites were strongly conserved.
The antituberculosis drug pyrazinamide (PZA) needs to be converted into pyrazinoic acid (POA) by the bacterial pyrazinamidase (PZase) in order to show bactericidal activity against Mycobacterium tuberculosis. M. avium is naturally resistant to PZA. To investigate whether this natural resistance to PZA is due to inability of the M. avium PZase to convert PZA to bactericidal POA, the M. avium PZase gene (pncA) was cloned by using the M. tuberculosis pncA gene as a probe. Sequence analysis showed that the M. avium pncA gene is 561 bp long, encoding a protein with a predicted size of about 19.8 kDa; but Western blotting showed that the M. avium PZase migrated as a 24 kDa band when expressed in M. bovis BCG and Escherichia coli. Sequence comparison revealed that M. avium PZase has 67.7% and 32.8% amino acid identity with the corresponding enzymes from M. tuberculosis and E. coli, respectively. Southern blot analysis with the M. avium pncA gene as a probe showed that M. terrae, M. gastri, M. marinum, M. fortuitum, M. xenopi, M. gordonae, M. szulgai, M. celatum and M. kansasii have close pncA homologues, whereas M. chelonae and M. smegmatis did not give significant hybridization signals. Transformation with the M. avium pncA gene conferred PZA susceptibility to PZA-resistant M. tuberculosis complex organisms, indicating that the nonsusceptibility of M. avium to PZA is not due to an ineffective PZase enzyme, but appears to be related to other factors such as transport of POA.
It was recently proposed that in rat pancreatic islets exposed to 8.3 mM D-glucose, alpha-D-glucose-6-phosphate undergoes enzyme-to-enzyme channelling between hexokinase isoenzyme(s) and phosphoglucoisomerase. To explore the identity of the hexokinase isoenzyme(s) involved in such a tunnelling process, the generation of 3HOH from the alpha- and beta-anomers of either D-[2-3H]glucose or D-[5-3H]glucose was now measured over 60 min incubation at 4 degrees C in pancreatic islets exposed only to 2.8 mM D-glucose, in order to decrease the relative contribution of glucokinase to the phosphorylation of the hexose. Under these experimental conditions, the ratio for 3HOH production from D-[2-3H]glucose/D-[5-3H]glucose at anomeric equilibrium (39.7 +/- 11.6%) and the beta/alpha ratios for the generation of 3HOH from either the D-[2-3H]glucose anomers (70.9 +/- 12.6%) or the D-[5-3H]glucose anomers (59.6 +/- 12.4%) indicated that a much greater fraction of alpha-D-glucose-6-phosphate escapes from the process of enzyme-to-enzyme channelling in the islets exposed to 2.8 mM, rather than 8.3 mM D-glucose. These findings suggest, therefore, that the postulated process of enzyme-to-enzyme channelling involves mainly glucokinase.
Rats depleted in long-chain polyunsaturated omega3 fatty acids (omega3-depleted rats) display several features of the metabolic syndrome including hypertension and cardiac hypertrophy. This coincides with alteration of the cardiac muscle phospholipid and triacylglycerol fatty acid content and/or pattern. In the present study, the latter variables were measured in the cardiac endothelium of normal and omega3-depleted rats. Samples derived from four rats each were obtained from 16 female normal fed rats and three groups of 36-40 female fed omega3-depleted rats each aged 8-9, 15-16 and 22-23 weeks. At comparable mean age, the ratio between the square root of the total fatty acid content of phospholipids and cubic root of the total fatty acid content of triacylglycerols was lower in omega3-depleted rats than in control animals. The total fatty acid content of triacylglycerols was inversely related to their relative content in C20:4omega6. Other differences between omega3-depleted rats and control animals consisted in a lower content of long-chain polyunsaturated omega3 fatty acids in both phospholipids and triacylglycerols, higher content of long-chain polyunsaturated omega6 fatty acids in phospholipids, higher activity of delta9-desaturase (C16:0/C16:1omega7 and C18:0/C18:1omega9 ratios) and elongase [(C16:0 + C16:1omega7)/(C18:0 + C18:1omega9) and C20:4omega6/C22:4omega6 ratios], but impaired generation of C22:6omega3 from C22:5omega3 in the former rats. These findings support the view that cardiovascular perturbations previously documented in the omega3-depleted rats may involve impaired heart endothelial function.
NMR well logging of petroleum reservoir require the measurement of the NMR response of water, oil, and gas in the pore space of rocks at elevated temperatures and pressures. The viscosity of the oil may range from less than 1 cp to greater than 10,000 cp. Also, the oil and gas are not a single component but rather a broad distribution of components. The log mean T1 and T2 relaxation time of dead (gas free) crude oils are correlated with viscosity/temperature and Larmor frequency. The relaxation time of live oils deviate from the correlation for dead crude oils. This deviation can be correlated with the methane content of the oil. Natural gas in the reservoir has components other than methane. Mixing rules are developed to accommodate components such as ethane, propane, carbon dioxide, and nitrogen. Interpretation of NMR logs uses both relaxation and diffusion to distinguish the different fluids present in the formation. Crude oils have a broad spectrum of components but the relaxation time distribution and diffusion coefficient distribution are correlated. This correlation is used to distinguish crude oil from the response of water in the pores of the rock. This correlation can also be used to estimate viscosity of the crude oil.
In this study, an in vitro multicellular tumor spheroid model was developed using microencapsulation, and the feasibility of using the microencapsulated multicellular tumor spheroid (MMTS) to test the effect of chemotherapeutic drugs was investigated. Human MCF-7 breast cancer cells were encapsulated in alginate-poly-l-lysine-alginate (APA) microcapsules, and a single multicellular spheroid 150 mum in diameter was formed in the microcapsule after 5 days of cultivation. The cell morphology, proliferation, and viability of the MMTS were characterized using phase contrast microscopy, BrdU-labeling, MTT stain, calcein AM/ED-2 stain, and H&E stain. It demonstrated that the MMTS was viable and that the proliferating cells were mainly localized to the periphery of the cell spheroid and the apoptotic cells were in the core. The MCF-7 MMTS was treated with mitomycin C (MC) at a concentration of 0.1, 1, or 10 times that of peak plasma concentration (ppc) for up to 72 h. The cytotoxicity was demonstrated clearly by the reduction in cell spheroid size and the decrease in cell viability. The MMTS was further used to screen the anticancer effect of chemotherapeutic drugs, treated with MC, adriamycin (ADM) and 5-fluorouracil (5-FU) at concentrations of 0.1, 1, and 10 ppc for 24, 48, and 72 h. MCF-7 monolayer culture was used as control. Similar to monolayer culture, the cell viability of MMTS was reduced after treatment with anticancer drugs. However, the inhibition rate of cell viability in MMTS was much lower than that in monolayer culture. The MMTS was more resistant to anticancer drugs than monolayer culture. The inhibition rates of cell viability were 68.1%, 45.1%, and 46.8% in MMTS and 95.1%, 86.8%, and 91.6% in monolayer culture treated with MC, ADM, and 5-FU at 10 ppc for 72 h, respectively. MC showed the strongest cytotoxicity in both MMTS and monolayer, followed by 5-FU and ADM. It demonstrated that the MMTS has the potential to be a rapid and valid in vitro model to screen chemotherapeutic drugs with a feature to mimic in vivo three-dimensional (3-D) cell growth pattern.
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