Browsing by Author "Chen, TS"

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A positive charge at position 33 of thioredoxin primarily affects its interaction with other proteins but not redox potential
(2004-02-03)
Lin, TY
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Chen, TS
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生物科技學系
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Department of Biological Science and Technology
Oxidoreductases of the thioredoxin superfamily possess the C-X-X-C motif. The redox potentials vary over a wide range for these proteins. A crucial determinant of the redox potential has been attributed to the variation of the X-X dipeptide. Here, we substitute Lys for Gly at the first X of Escherichia coli thioredoxin to investigate how a positive charge would affect the redox potential. The substitution does not affect the protein's redox potential. The equilibrium constant obtained from pairwise reaction between the mutant and wild-type proteins equals 1.1, indicating that the replacement does not significantly affect the thiol-disulfide redox equilibrium. However, the catalytic efficiency of thioredoxin reductase on the G33K mutant decreases approximately 2.8 times compared to that of the wild type. The mutation mainly affects K-m, with little effect on k(cat). The mutation also inhibits thioredoxin's ability to reduce insulin disulfide by approximately one-half. Whether the mutant protein supports the growth of phages T3/7 and f1 was tested. The efficiency of plating (EOP) of T3/7 on the mutant strain decreases 5 times at 37 degreesC and 3 x 10(4) times at 42 degreesC relative to that of the wild-type strain, suggesting that interaction between phage gene 5 protein and thioredoxin is hindered. The mutation also reduces the EOP of phage f1 by 8-fold at 37 degreesC and 1.5-fold at 42 degreesC. The global structure of the mutant protein does not change when studied by CD and fluorescence spectra. Therefore, G33K does not significantly affect the overall structure or redox potential of thioredoxin, but primarily interferes with its interaction with other proteins. Together with the G33D mutation, the overall results show that a charged residue at the first X has a greater influence on the molecular interaction of the protein than the redox potential.
Combined carrier phase tracking and equalization for pi/4-DQPSK signals in mobile radio
(1999)
Chen, TS
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Liu, DZ
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Wei, CH
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電子工程學系及電子研究所
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Department of Electronics Engineering and Institute of Electronics
The digital sinlock loop (DSL) is a nonuniform-sampling digital phase-locked loop (DPLL), whose phase error detector using the arcsine function with the quadrature samples of incoming signal, has a linear characteristics with a period of 2 pi. The phase equalizer using the decision-feedback phase tracking method operates only on the phase information to avoid the multiplication operations required in conventional equalization algorithms. In this paper, combined carrier phase tracking and phase equalization is investigated for pi/4-DQPSK signals in the mobile radio system.
Cross interactions on interfacial compound formation of solder bumps and metallization layers during reflow
(2004-12-01)
Shao, TL
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Chen, TS
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Huang, YM
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Chen, C
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材料科學與工程學系
While the dimension of solder bumps keeps shrinking to meet higher performance requirements, the formation of interfacial compounds may be affected more profoundly by the other side of metallization layer due to a smaller bump height. In this study, cross interactions on the formation of intermetallic compounds (IMCs) were investigated in eutectic SnPb, SnAg3.5, SnAg3.8Cu0.7, and SnSb5 solders jointed to Cu/Cr-Cu/Ti on the chip side and Au/Ni metallization on the substrate side. It is found that the Cu atoms on the chip side diffused to the substrate side to form (Cu-x,Ni1-x)(6)Sn-5 or (Ni-y,Cu1-y)(3)Sn-4 for the four solders during the reflow for joining flip chip packages. For the SnPb solder, Au atoms were observed on the chip side after the reflow, yet few Ni atoms were detected on the chip side. In addition, for SnAg3.5 and SnSn5 solders, the Ni atoms on the substrate side migrated to the chip side during the reflow to change binary Cu6Sn5 into ternary (Cu-x,Ni1-x)(6)Sn-5 IMCs, in which the Ni weighed approximately 21%. Furthermore, it is intriguing that no Ni atoms were detected on the chip side of the SnAg3.8Cu0.7 joint. The possible driving forces responsible for the diffusion of Au, Ni, and Cu atoms are discussed in this paper.