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A nice clip i found on the mechanisms of action of topoisomerase 1 and 2.


Topoisomerase I cuts one strand in the double-stranded DNA and no ATP is required for its function. On the other hand Topoisomerase, II cuts both strands in DNA and needs ATP for its activity. This is the key difference between Topoisomerase I and II. CONTENTS. 1. Overview and Key Difference 2. What is Topoisomerase I 3. What is Topoisomerase II 4.


Discovery. In the 1970s, James C. Wang was the first to discover a topoisomerase when he identified E. coli topoisomerase I. Topo EC-codes are as follows: type I, EC; type II: EC Function. The overall function of DNA topoisomerase is to manage the topological state of the DNA in the cell. There are two types or families of this enzyme; type I family and type II family.


The human topoisomerase type IB enzyme forms a covalent 3'-phosphotyrosine intermediate, the topoisomerase 1-cleavage-complex (Top1cc). The active irinotecan metabolite, SN-38, acts by trapping (making a ternary complex with) a subset of Top1cc, those with a guanine +1 in the DNA sequence.


Type I topoisomerase cuts one strand of a DNA double helix and then reanneals the cut strand. Type I topoisomerases are subdivided into two subclasses: type IA topoisomerases which share many structural and mechanistic features with the type II topoisomerases, and type IB topoisomerases, which utilize a controlled rotary mechanism.


Figure 01: Topoisomerase I and II The Ecoli topoisomerase I is a holoenzyme with three Zn (II) atoms in the tetracysteine motifs near its carboxy terminus. It is 97 kDa in weight. Topoisomerase I has several unusual features. It does not need ATP hydrolyzing to catalyze the topological rearrangement of DNA.


2 μl 10× topoisomerase II reaction buffer. 5 nM supercoiled plasmid DNA. 1 to 2 μl of test agent or positive control. H 2 O was added to bring the final reaction volume to 20 μl (including the volume of enzyme to be added in step 2). Add 1 to 2 μl of 4 to 20 U/μl topoisomerase II (0.1 to 1 μg purified protein).


Box 1. Many different classes of compounds target Topoisomerase II. Drugs targeting topoisomerase II fall into two categories, Top2 poisons and Top2 catalytic inhibitors. Many Top2 poisons have demonstrated anti-cancer activity. Top2 poisons can be further sub-divided into intercalating and non-intercalating poisons.


It is a weak topoisomerase II inhibitor and forms stable DNA adducts through alkylation with specificity for DNA hypermethylated sites. S3603: Betulinic acid. Betulinic acid, a pentacyclic triterpenoid from Syzigium claviflorum, is a inhibitor of HIV-1 with EC50 of 1.4 μ M. Betulinic acid acts as a new activator of NF-kB.Phase 1/2.