Epinephrine modulates cellular distribution of muscle phosphofructokinase.

In this paper, we report evidences that cellular distribution of phosphofructokinase can be affected by epinephrine stimulation in rabbit skeletal muscle homogenates. Through co-sedimentation techniques, we observed that in epinephrine-stimulated tissues, approximately 50% of phosphofructokinase activity is co-located in an actin-enriched fraction, against 29% in control. This phenomenon is accompanied by a 400% increase in specific phosphofructokinase activity in stimulated homogenates. This effect is reproduced by the beta-adrenergic agonist isoprenaline. Here we propose that the modulation of cellular distribution of phosphofructokinase may be one of the mechanisms of control of glycolytic flux in mammalian muscle, by beta-adrenergic stimulation.

Regulation of fructose uptake and catabolism by succinate in Azospirillum brasilense.

Fructose uptake and catabolism in Azospirillum brasilense is dependent on three fructose-inducible enzymes (fru-enzymes): (i) enzyme I and (ii) enzyme II of the phosphoenolpyruvate:fructose phosphotransferase system and (iii) 1-phosphofructokinase. In minimal medium containing 3.7 mM succinate and 22 mM fructose as sources of carbon, growth of A. brasilense was diauxic, succinate being utilized in the first phase of growth and fructose in the second phase with a lag period between the two growth phases. None of the fru-enzymes could be detected in cells grown with succinate as the sole source of carbon, but they were detectable toward the end of the first phase of diauxie. All the fru-enzymes were coinduced by fructose and coordinately repressed by succinate. Studies on the effect of succinate on differential rates of syntheses of the fru-enzymes revealed that their induced syntheses in fructose minimal medium were subject to transient as well as permanent (catabolite) repression by succinate. Succinate also caused a similar pattern of transient and permanent repression of the fructose transport system in A. brasilense. However, no inducer (fructose) exclusionlike effect was observed as there was no inhibition of fructose uptake in the presence of succinate with fructose-grown cells even when they were fully induced for succinate uptake activity.