Biomedical subjects

C C Teng

Publications and source records attributed to C C Teng.

At least 19 recordsLinked to original sources

PubMed2001

Quantitative feedback synthesis of sampled-data systems with time-delay by approximate Z-transform.

In this paper, the equivalent disturbance rejection (EDR) in QFT design methodology is proposed for dealing with sampled-data systems with time-delay. This EDR is mainly to overcome the non-minimum phase zero generated by the first order Pade' approximation of the time-delay factor. Due to plant parameter uncertainty, the analogue controller is to be designed so that the system response lies within permissible bounds. By approximate Z-transform, the analogue controller can be transformed directly into a digital one and then the analogue plant is transformed into the digital plant, with sampling time as a free parameter. By adjusting the sampling time, the uncertain sampled-data system can be stabilized. In comparison with other approaches, our design framework is much more systematic by using only algebraic manipulations and transparent enough to guide the designer to realize the physical controller for the plant with prescribed bounds on its parameters.

Journal Article↗

PubMed1999

Conformational changes of polyomavirus major capsid protein VP1 in sodium dodecyl sulfate solution.

Conformations of polyomavirus (Py) major capsid protein VP1 were analyzed by circular dichroism (CD) and fluorescence spectroscopy in the presence of sodium dodecyl sulfate (SDS). Binding of PyVP1 to SDS induced marked conformational changes of PyVP1, which were reflected on the CD and fluorescence spectra. Abrupt changes in both optical properties occurred within the narrow ranges of SDS concentrations with the transition midpoints closely related to SDS micelle formation. Analysis of circular dichroism spectra showed that the contents of alpha-helices, beta-sheets, beta-turns and random coils in PyVP1 varied upon addition of SDS, demonstrating the exquisite sensitivity of the conformations of the protein to the environment. The interactions of PyVP1 with SDS were shown to be dependent on the ionic strength of the protein solution, suggesting that both hydrophobic and electrostatic forces contribute to the PyVP1-SDS complex formation. The SDS-induced conformational changes of PyVP1 appeared to be a two-stage process.

Capsid↗

PubMed1998

Stability of polyomavirus major capsid protein VP1 under denaturants guanidine hydrochloride and urea.

The guanidine hydrochloride (GdnHCl)- and urea-induced equilibrium denaturation of recombinant polyomavirus (Py) major capsid protein VP1 was studied by circular dichroism and fluorescence spectroscopy. Both secondary and tertiary structures of PyVP1 were shown to be disrupted in the presence of denaturants. Although the far-UV circular dichroism (CD) spectra of PyVP1 in the denaturants exhibit similar two-phase transition as those obtained from the fluorescence measurements, the unfolding of PyVP1 in GdnHCl was shown to be more complex than a similar two-state mechanism. The presence of unfolding intermediates is manifested by the noncoincidence of transitions when detected by different probes. The unfolding intermediate appeared to be stabilized by 1 M NaCl. Addition of Ca2+ and 2-mercaptoethanol does not show significant effect on the conformational stability of PyVP1. Unfolding of PyVP1 in GdnHCl was shown to be an irreversible process.

Capsid↗

PubMed1998

Circular dichroism and fluorescence studies of polyomavirus major capsid protein VP1.

The conformational changes of polymavirus (Py) major capsid protein VP1 in solution by the solution pH, addition of calcium, and ionic strength were examined by circular dichroism (CD) and fluorescence spectroscopy. Comparison of the predicted secondary structures of PyVP1 and simian virus (SV) 40 by the methods of Chou-Fasman, Garnier et al., and Yang method are presented. Hydropathicity, surface probability, and chain flexibility of PyVP1 were computer-analyzed by the methods of Kyte and Doolittle, Emini et al., and Karplus and Schulz, respectively. The CD measurements indicate that the secondary structure of PyVP1 is little dependent on its concentration, Ca2+ concentration, and ionic strength, but is strongly pH dependent. Fluorescence studies showed that emission spectra of PyVP1 are also pH-dependent. At extreme acidic and alkaline pH, the fluorescence intensity of PyVP1 is decreased and the emission maximum is red-shifted. The fluorescence of PyVP1 is quenched by the presence of CsCl, KI, and acrylamide. The analyses of the modified Stern-Volmer plots indicate that five of seven tryptophan residues in PyVP1 are located on the surface of the protein, among which two are accessible to Cs+ and the other three are accessible to I- . The two others are buried more deeply in the interior of the protein molecule.

Acrylamide↗

PubMed1997

Leucine metabolism in chronically hypoglycemic hypoinsulinemic growth-restricted fetal sheep.

We measured leucine flux rates during infusions of L-[1-14C]- and L-[1-1C]leucine in fetal sheep exposed to maternal insulin-induced hypoglycemia over the last 8 wk (40%) of gestation to determine effects of chronic glucose deficiency and hypoglycemia on fetal leucine metabolism. Compared with control fetuses (C, n = 5), hypoglycemic fetuses (HG, n = 8) weighed less (C, 3.43 +/- 0.07 kg; HG, 2.32 +/- 0.24 kg), had lower plasma glucose (C, 1.04 +/- 0.02 mM; HG, 0.59 +/- 0.01 mM), insulin (C, 48 +/- 6 pM; HG, 12 +/- 6 pM), and leucine concentrations (C, 195.6 +/- 8.3 microM; HG, 140.8 +/- 15.0 microM), lower rates of net leucine uptake (C, 4.2 +/- 0.6 mumol.min-1.kg-1; HG, 2.1 +/- 0.4 mumol.min-1.kg-1) and leucine flux into protein accretion (C, 2.8 +/- 0.2 mumol.min-1.kg-1; HG, 0.6 +/- 0.1 mumol.min-1.kg-1), and an increased rate of leucine release from protein breakdown (C, 1.1 +/- 0.1 mumol.min-1.kg-1; HG, 3.3 +/- 0.2 mumol.min-1.kg-1) (P < 0.05 for all). Plasma leucine disposal, flux into protein synthesis, and oxidation were not different between groups. We conclude that adaptations of fetal leucine metabolism to long-term hypoglycemia and decreased glucose apply represent diminished leucine uptake and increased leucine release from protein breakdown, which are associated with decreased incorporation of leucine into protein accretion and a slower rate of fetal growth.

Animals↗

PubMed1990

Versatile stable isotope technique for the measurement of amino acids and keto acids: comparison with radioactive isotope and its use in measuring in vivo disposal rates.

Tracer methods using both carbon-13 and -14 have been utilized for determination of ovine fetal amino acid disposal and the results compared in seven animals. We infused [1-13C]leucine simultaneously with [1-14C]leucine into the fetal circulation of pregnant sheep chronically catheterized during late gestation. Radioactive and stable isotope enrichments of leucine (Leu) and stable isotope enrichments of ketoisocaproic acid (KIC) in the umbilical artery and vein and the maternal artery and uterine vein were measured. Stable isotope enrichments and concentrations of both Leu and KIC were determined from a single 0.2-ml sample by the use of internal standards and electron ionization GC/MS analysis after a simple isolation and derivatization procedure. The KIC/Leu enrichment ratio was measured for the first time in fetal arterial plasma and was 0.66 +/- 0.05 (SE). Fetal leucine disposal rate was 9.0 +/- 0.5 (SE) micron/min/kg. Disposal rates determined by stable isotopes were not different from those determined by radioactive isotopes. The GC/MS stable isotope method provided higher precision in both leucine concentration and enrichment measurements and has been shown to be a general method for the determination of concentration and isotopic enrichment of other amino acids and their corresponding keto acids. Furthermore, this method is ideally suited to clinical studies where large numbers of samples of rather small volume can easily be studied with a short turnaround time.

Amino Acids↗

PubMed1975