Quantitative studies on the flavins in the soluble fractions of heavy mitochondria of rat liver

Effects of paraoxon and ethylparathion on choline oxidase from Alcaligenes species: Inhibition and denaturation

The kinetics and thermodynamics of the effects of paraoxon (POX) and ethylparathion (EPA) on choline oxidase (ChOx) were studied. Lineweaver-Burk plots of initial velocity data showed a parallel pattern indicating uncompetitive inhibition versus choline. The inhibition constant (K(I)) obtained from the secondary plots for POX and EPA were 0.14+/-0.01 and 0.48+/-0.05 mM, respectively, suggesting that POX is a more potent inhibitor of ChOx than EPA. UV absorption was used to monitor the denaturation of ChOx by POX and EPA. A decrease in FAD fluorescence associated with the interaction of POX and EPA with ChOx suggested a tertiary structural change. Interaction of the enzyme molecule with POX or EPA resulted in inhibition and subsequently denaturation of the enzyme. The results indicate that inhibition and denaturation of the enzyme by POX and EPA are linked, but not parallel events, with inhibition occurring at lower concentrations with respect to denaturation. This suggests that the loss of initial velocity of the enzyme is an active site specific effect and not due to global conformational changes induced by the inhibitors.

Binding of inorganic mercury by subcellllar fractions and proteins of rat kidneys

Inorganic mercury, administered to rats in a single dose of 0.5 mg Hg/kg is accumulated in the kidneys mainly in the soluble (54%) and nuclear (30%) fractions, showing decreasing tendency with time. Mitochondrial and microsomal fractions, initially accumulating approx. 11 and 6% of total Hg, show a tendency to increase the absolute level of Hg for the first week after administration. In the soluble fraction low-molecular weight, metallothioneinlike proteins are mainly responsible for the accumulation of mercury, in other fractions proteins of higher molecular weight prevail.