A thermodynamic study of self-association in β-casein and Brij 35 solutions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Chemistry at Massey University, New Zealand

The self-association of both β-casein A1 and Brij 35 in aqueous solution has been studied at several temperatures using the techniques of microcalorimetry, sedimentation equilibrium, sedimentation velocity, pycnometry and surface tension measurements. Attempts to obtain the equilibrium concentration of the various β-casein species in solution by ultracentrifugation have been unsuccessful owing to both degradation and the rate of equilibration. The equilibrium concentrations for β-casein were estimated from published fluorescence data. The results have been analysed by treating each self-association process as being one of micelle formation. For both systems the standard free energy of micelle formation was negative whereas the corresponding standard enthalpy and entropy changes were positive. The temperature trends in the various thermodynamic parameters were inconclusive owing to experimental uncertainty. The significance of the values of the thermodynamic parameters is discussed qualitatively. The driving force behind the self-association process for both systems appears to be the positive entropy change associated with the hydrophobic effect. A compàrison is made between the two systems and it is concluded that β-casein self-association is similar in several respects to micelle formation in solutions of synthetic detergents

The primary hydrogen kinetic isotope effect in the elimination from 2-phenethyl systems : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science with Honours in Chemistry at Massey University

Some Dutch language throughoutThe primary kinetic isotope effects for the base-catalysed E2 elimination from a series of substituted 2-phenethyl bromides and 2-phenethyldimethylsulphonium bromides in dimethyl sulphoxide-water as solvent at 20° have been measured. A broad maximum in the isotope effect was observed for the 2-phenethyl bromides. The Hammett p value for each reaction series at 20° has also been determined and both were large and positive. Arrhenius plots using the kH/kD ratios for each of the p-MeO substituted compounds at 20°, 30° and 40° were carried out to determine the importance of proton tunnelling in these reactions. The usefulness of the primary Kinetic isotope effect as a measure of proton position in the E2 transition states for these reactions is discussed

The mesa trail and the interacting heads motif of myosin II

Myosin II molecules in the thick filaments of striated muscle form a structure in which the heads interact with each other and fold back onto the tail. This structure, the interacting heads motif (IHM), provides a mechanistic basis for the auto-inhibition of myosin in relaxed thick filaments. Similar IHM interactions occur in single myosin molecules of smooth and nonmuscle cells in the switched-off state. In addition to the interaction between the two heads, which inhibits their activity, the IHM also contains an interaction between the motor domain of one head and the initial part (subfragment 2, S2) of the tail. This is thought to be a crucial anchoring interaction that holds the IHM in place on the thick filament. S2 appears to cross the head at a specific location within a broader region of the motor domain known as the myosin mesa. Here, we show that the positive and negative charge distribution in this part of the mesa is complementary to the charge distribution on S2. We have designated this the mesa trail owing to its linear path across the mesa. We studied the structural sequence alignment, the location of charged residues on the surface of myosin head atomic models, and the distribution of surface charge potential along the mesa trail in different types of myosin II and in different species. The charge distribution in both the mesa trail and the adjacent S2 is relatively conserved. This suggests a common basis for IHM formation across different myosin IIs, dependent on attraction between complementary charged patches on S2 and the myosin head. Conservation from mammals to insects suggests that the mesa trail/S2 interaction plays a key role in the inhibitory function of the IHM

The prevalence and progression of autoimmune thyroid disease in the elderly

Thyroid antibodies were measured by an enzyme-linked assay system (ELISA) on a random sample of 414 asymptomatic elderly people aged 70 years or more in a South Wales town in 1977. The prevalence of elevated titres of microsomal antibodies was 15.4% and of thyroglobulin antibodies 13.3%; 8.5% had an elevation of both antibodies. Five years later thyroid function was evaluated in 51 (66.6%) of those people with raised antibody titres in 1977 and compared with a control group of 46 old people drawn from the original population. Significant fluctuations of microsomal and thyroglobulin antibody titres were observed in two thirds of the antibody positive group. Three people in the control group developed positive thyroid antibodies during this period. Only 1 person in the antibody positive group became hypothyroid. The prognostic significance of raised thyroid antibodies with or without elevated TSH levels is less in the elderly than in middle aged or younger people. The significance of the fluctuating antibody levels as measured by a more sensitive method remains to be determined

Systems Pharmacology Modeling Predicts Delayed Presentation and Species Differences in Bile Acid–Mediated Troglitazone Hepatotoxicity

Troglitazone (TGZ) caused delayed, life-threatening drug-induced liver injury (DILI) in some patients, but was not hepatotoxic in rats. This study investigated altered bile acid (BA) homeostasis as a mechanism of TGZ hepatotoxicity using a systems pharmacology model incorporating drug/metabolite disposition, BA physiology/pathophysiology, hepatocyte life cycle, and liver injury biomarkers. In the simulated human population, TGZ (200–600mg/day×6months) resulted in delayed increases in serum ALT>3× ULN in 0.3–5.1% of the population with concomitant bilirubin elevations>2× ULN in 0.3–3.6%. In contrast, pioglitazone (15–45mg/day×6months) did not elicit hepatotoxicity, consistent with clinical data. TGZ was not hepatotoxic in the simulated rat population. In summary, mechanistic modeling based only on BA effects accurately predicted the incidence, delayed presentation, and species differences in TGZ hepatotoxicity, and the relative liver safety of pioglitazone. Systems pharmacology models integrating physiology and experimental data can evaluate DILI mechanisms and may be useful to predict hepatotoxic potential of drug candidates