In this work the micro.somal laurie acid a~-hydroxylation, fatty acid peroxisomalfl-oxidation, and the levels ofcytochrome P-450 IVAI were studied in liver tissu¢ from ,starved rats. Starvation increased the peroxisomal S-oxidation and the microsomal hydroxylation of fatty acids. The correlation between these activities would .support the proposal that both processes are linked, contributing in part to catabolism of fatty acids in liver of starvgl rats.

Stop flow pH jump experiments were carried out on poly(methacrylic acid), PMA, solution of various molecular weights. The fluorescence changes of the probe pyrene, which can locate in the hydrophobic PMA coil or in the aqueous phase, were used to monitor pH-induced events in the PMAwater system. At least two well-separated time regions for the pH-induced conformational change of PMA were observed: one with τ ) 1-2 s and another with τ ) 50-100 s. A theoretical model to quantitatively explain the observed kinetic changes is given. This is based on a model developed by Schwarz for the helix-coil transition of polypeptides and can be briefly described as follows. Any configuration of the polymer is characterized by a statistical distribution of segments in polar and hydrophobic regions. Then a conformational transition involves the change of a number of segments from one state to the another, and its kinetics corresponds to a relaxation process with the pH jump as the initial perturbation. Several details pertinent to unambiguous interpretation are also described briefly. This includes the rate of neutralization of the acid groups on PMA and the rate of solution of small pyrene crystals in a colloidal system. The above confusing effects were established and thus could be avoided in the actual pH-induced conformational changes of PMA.

The kinetics of fluorescence quenching of pyrene and three of its derivatives by a series of n-alkylpyridinium ions has been studied. The quenching process is diffusion controlled for all the systems studied, independent of the charge in the aromatic molecule and the size of the alkyl chain in the pyridinium ions. Pyrensulfonate, PS, and pyranine form ground-state complexes with these quenchers. The association constants were determined by using a kinetic scheme where both dynamic and static quenching were included. A linear relationship between the free energy change and number of carbon atoms was found for PS, and a methylene contribution equal to -1.1 kJ/mol was determined from the slope. A similar correlation was established for pyranine, but a slope change was observed when the alkyl chain has more than 10 carbon atoms. From the initial slope, an incremental free energy of -0.35 kJ/mol was obtained. The ground-state complex formation is determined mainly by an electrostatic interaction, but there is a hydrophobic effect on the value of the measured association constants.

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