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Thesis (Ph. D.)--University of Hong Kong, 2007. / Also available in print.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Medicine / Master / Master of Medical Sciences

Cyclopropenoid fatty acids (CPFA) are unique compounds that contain a highly strained and reactive cyclopropene ring structure. These compounds have been shown to cause a number of toxic effects in a variety of animals. Rainbow trout (Salmo gairdneri) have proven to be particularly sensitive to CPFA. Studies have revealed that CPFA are both carcinogenic and cocarcinogenic in rainbow trout. However, the mechanism(s) of these adverse biological effects are not understood. In the present report a series of studies were performed in order to determine the effect of CPFA on the levels and synthesis rates of trout hepatocyte proteins. In the first study, the influence of dietary CPFA on protein synthesis was measured via the use of amino acid double labeling experiments in isolated hepatocytes. Both the microsomal and cytosolic subcellular fractions were examined in these studies after separation by lithium dodecyl sulfate polyacrylamide gel electrophoresis. In the cytosolic fraction, the synthesis of proteins with apparent molecular weights in the range of 68,000 to 74,000 were significantly decreased. A marked depression in both the level and synthesis rate of microsomal proteins was observed for proteins that migrate in the 200,000 to 240,000 relative molecular mass region in polyacrylamide gels. These high molecular weight proteins do not appear to be membrane proteins and one of them has biotin associated with it. Using avidin-peroxidase staining, it was shown that the mass of this protein was reduced in CPFA-fed trout by 80%. The possible identity of these proteins is discussed. In the second study, initial attempts were made to use two dimensional gel electrophoresis to study alterations in individual liver microsomal polypeptides from trout fed CPFA. In order to effectively resolve membrane proteins in the first dimension (isoelectric focusing) changes in the standard techniques were needed. Replacement of the detergent nonidet-40 with 3-[(3-cholamidopropyl)dimethylammonio]-l-propane sulfonate (CHAPS) in isoelectric focusing of trout liver microsomes have greatly increased resolution. These results have allowed effective resolution of complex polypeptide patterns for comparative purposes. In the third study, antibodies against β-napthoflavone-fed rainbow trout cytochrome P-450 (LM₂) were employed to localize the corresponding polypeptide(s) via protein blotting and immunochemical staining. Microsomes isolated from β-napthoflavone-fed trout contained only a single polypeptide. In contrast, control microsomes contained two distinct polypeptides differing only in their isoelectric points. Thus, an additional P-450 isozyme in rainbow trout was tentatively identified. CPFA treatment caused a preferential decrease in only one of the isozymes found in the control samples. The presence of concanavalin A binding glycopolypeptides was determined. The two P-450 isozymes localized on control microsomal gels were found to bind concanavalin A, suggesting that these isozymes are giycoproteins. Another result of CPFA treatment was a shift in a closely related group of membrane glycopolypeptides, labeled gp80, gp82, gp80₁, and gp82₁. A decrease in the mass of gp80 and gp82, and a corresponding increase in mass of gp80₁ and gp82₁ was observed. / Graduation date: 1985

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No description available.

Flow through an experimental model of a U-shaped flow channel is used to investigate the hydrodynamic phenomena that occur within serpentine reactant transport channels of fuel cells. Achieving effective mixing within these channels is crucial for the proper operation of the fuel cell and proper understanding and characterization of the underlying fluid dynamics is required. Particle image velocimetry (PIV) is used to investigate the three-dimensional structure of the flow by analyzing the velocity and associated vorticity field over two perpendicular channel cross-sections. A range of Reynolds numbers, 109 I Re I 872, corresponding to flow rates encountered in a fuel cell operating at low to medium current densities is investigated. The effect of the flow rate is characterized in terms of the instantaneous and time-averaged representations of the velocity vectors, out-of-plane vorticity and the velocity streamlines. At the lowest Reynolds numbers, the flow is steady and is characterized by high vorticity regions associated with shear layers separating from the sharp convex comers of the U-bend and reattaching on downstream surfaces. The flow also exhibits the classical secondary Dean flow pattern with two symmetric circulation zones. Transition takes place in the range 381 I Re I 436 as the two recirculation zones, which originally develop in the U-bend region, merge into one separation region. This transition is accompanied by the generation of additional vortices in the secondary flow plane. The relationship between the flow in both planes and the transition is examined along with properties of the instability including RMS, Reynolds stress, and the oscillation frequency. The quantitative flow visualization results obtained presented here should be useful in guiding numerical models of fuel cells, and indicate that the commonly used assumption of steady laminar flow should be revisited, and alternative models developed.

No description available.