If "k" inhibits activity of enzyme "5", then enzyme "5" is under control. if enzyme "3" becomes activated in response to activity of protein kinase a only when compound "a" is present, then enzyme "3" is under control. if enzyme "2" is only expressed in the presence of high concentrations of "a," then enzyme "2" is under control. if all of these are true, high concentrations of "__" will decrease the flux through the pathway.