1. The antihypercholesterolaemic drug ethyl alpha-p-chlorophenoxyisobutyrate when fed to the rat orally or mixed with the diet increased the content of mitochondria in the liver by 50-100%. Other subcellular fractions did not show any significant change. 2. In oxidative activity, respiratory control and phosphorylating ability no significant difference was observed between the mitochondria isolated from the livers of the drug-treated rats and those from normal animals. 3. In agreement with earlier reports, administration of the drug depressed the concentration of serum cholesterol and increased liver weight and the liver content of ubiquinone. However, the increase of ubiquinone was greater in the nuclear than in the mitochondrial protein.
1. On brief exposure of rats to hypobaric conditions, the activity of hepatic mitochondrial succinate dehydrogenase was raised from the basal state to a ;partially activated state'. This was further raised to ;fully activated state' by preincubation of mitochondria with succinate, as was the activity in mitochondria from normal rats. 2. On washing mitochondria with the homogenizing sucrose medium the activity excess obtained on preincubation with succinate was lost in mitochondria from both normal and treated rats. 3. The enzyme in the ;partially activated state' from animals exposed to hypobaric conditions was stable to the washing procedure but was labilized and reverted to a low basal state of activity on freezing and thawing of the isolated mitochondria. 4. The results suggest that activation of succinate dehydrogenase under hypobaric conditions represents a conformational change leading to a stable, partially activated, form of the enzyme system: this is the first evidence of physiological modulation of this rate-limiting step in the control of the rate of oxidation of succinate.
Stimulation of glyceraldehyde-3-phosphate dehydrogenase (G3PD) activity and accelerated growth occur in cultures of monkey kidney epithelial cells (BSC-1 line) that are exposed to medium with a reduced K concentration (3.2 mM). We recently found that this activation of G3PD was mediated by the appearance of a new cytosolic protein with an apparent molecular weight of 62,000. G3PD and this modifier protein were isolated from BSC-1 cells, and the interaction between them was characterized to define the mechanism(s) of enzyme activation. The enzyme protein was purified from cells grown in control medium (5.4 mM K). The enzyme, in the presence of modifier, exhibited an increase in maximal rate of enzyme reaction and a decrease in the apparent Km for NAD+. Analysis using Dixon plots revealed that the presence of modifier increased the Ki for NADH by two- to threefold. Inhibition by NADH was competitive with respect to NAD+, glyceraldehyde-3-phosphate, and inorganic phosphate. ATP also inhibited enzyme activity in a competitive manner with respect to NAD+; however, the Ki for ATP was similar both in the presence and absence of modifier. These results suggest that one mechanism by which the cytosolic modifier protein stimulates G3PD activity is to decrease product inhibition by NADH.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.