he synthesis of a phosphodiester bond involves condensation of a5'- phosphoryl group on one nucleotide with a 3' hydroxyl group onan adjacent nucleotide. DNA Ligases catalyze this reaction bycoupling condensation to cleavage of a phosphoanhydride bond fromeither NAD+ or ATP.
The overall reaction catalyzed by T4 DNA ligase is seen in thisequation:
ATP + nicked bond -> AMP + PPi +phosphodiester bond
This is actually the sum of two half reactions. The sum of ahydrolysis reaction coupled to a condensation reaction isthermodynamically equivalent to the ligase reaction represented bythe overall reaction (above).
Why does the ratio of nicked to diester bonds increase as more AMPis added to the system?