Type I Topoisomerase - Intermediates

Intermediates

All topoisomerases form a phosphotyrosine intermediate between the catalytic tyrosine of the enzyme and the scissile phosphoryl of the DNA backbone.

• Type IA topoisomerases form a covalent linkage between the catalytic tyrosine and the 5'-phosphoryl.
• Type IB enzymes form a covalent 3'-phosphotyrosine intermediate.
• Type 1C topoisomerases form a covalent 3'-phosphotyrosine intermediate.

This intermediate is isoenergetic, meaning that the forward cleavage reaction and the backward religation reaction are both energetically equal. As such, no outside energy source is necessary to conduct this reaction.