Which statement is true regarding the regulation of nitrogen fixation?
1) High concentrations of ADP will activate nitrogen fixation enzymes.
2) Elevated concentrations of ammonia will reduce expression of genes associated with nitrogen fixation.
3) ATP acts as a negative allosteric effector for nitrogenase.
4) Nitrogenase is regulated via adenylylation.
5) Oxygen acts as an allosteric effector for the nitrogenase complex.