Question

4. The X-fold increase in [AMP] (resulting from a 10% decrease in [ATP]) can be shown to be responsible for about a 9 told increase in flux through glycolysis by its action on phosphofructokinase alone. But a 9-fold increase is still not an -fold increase, so there must be something more to the story. That "something more" includes substrate cycling (see Figure 15-25 in your text). The reaction catalyzed by fructose-1,6-bisphosphatase (FBPase) acts as the reverse direction reaction for the reaction catalyzed by phosphofructokinase (PFK), which acts as the forward direction reaction. Thus, flux (J), which equals vr-v, can be regulated by independently regulating these two reactions. The X fold increase in [AMP] can increase vr by increasing the activity of PFK (as an allosteric activator) and simultaneously (a) Let's first assume that this X-fold increase in [AMPI mcreases PFK activity (eg increases vi) from 10% of its is known to be about 10-fold greater than the maximum value of FBPase activity. Therefore, if we arbitrarily decrease vi by decreasing the activity of FBPase (as an allosteric inhibitor). maximum value to 90% of its maximum value. At the same time, it decreases FBPase activity (eg, decreases v maximum value to 10% of its maximum value. Empirically, the maximum value o assign 100 units to be the mi imum value of PFK activity, wha would be the values of PFK activity at 90% (high AMP) and 10% (low [AMP]) of this maximum? What would be the relative values of FBPase activity at 90% (l ow [AMP) and 10% (high [AMP) of its maximum? The table below will help you organize this. (4 pts) PFK activity FBPase activity Low [AMP) High [AMP] The lowest flux in the forward direction under conditions of low [AMP] is: (b) o vlow [AMPT)-V(low [AMP), The highest flux in the forward direction under conditions of high [AMP] is: Jriph Vy(high [AMPT)-V(high [AMP). What are the values of Jhow and Jrigh? (2 pts) What -fold increase is realized using substrate cycling? (2 pts) (c) he ng

Answer 1

The X - fold increase in can be shown to be responsible for about a 9 - fold increase in flux through glycol sis by its action on phosphor fructokinase along. * But a 9 - fold increases is still not an 100 - fold increase, so there must be something more to the story *The x - fold increase in can increase v_f by increasing the activity of PEK and simultaneously. (a) Let us assume first, rightarrow X - fold increase in [AmP] increases PFK activity from 10% of its maximum value to 90% of its maximum value. rightarrow At the same time, it decrease FBpase activity from 90% of its maximum value to 10% of its maximum value. \r\n Here, Amp 10% rightarrow 90%} rightarrow increases FBpase 90% rightarrow 10%}decreases. from the above table, 10 - fold PEK activity > maximum value of FBpase. (b) The lowest flux in the forward direction under conditions of low [AMP] is, J_low = v_f (low[AMP]) - v_r(low[AMP]