The effects of dephosphorylation on human placental DNA topoisomerase I (Topo I) activity have been investigated.
The Topo I activity reduced to 75, 70, 50 and 10% in comparison with that of control by 2.5, 5, 10 and 20 units of calf intestinal alkal...
The effects of dephosphorylation on human placental DNA topoisomerase I (Topo I) activity have been investigated.
The Topo I activity reduced to 75, 70, 50 and 10% in comparison with that of control by 2.5, 5, 10 and 20 units of calf intestinal alkaline phosphatase (CIP) for 30 min treatment, respectively. And the enzyme activity was not changed by 20 units of CIP for 5 min treatment but dramatically reduced over 10 min. Both purified Topo I and partially dephosphorylated Topo I activity were not changed by protein kinase A for 30 minutes at 37℃, The inhibitory effects of Camp on both purified Topo I and partially dephosphorylated Topo I were identical.
These results suggest that Topo I purified from human placenta is already phosphorylated and its activity can be regulated by phosphorylation/dephosphorylation. And Topo I might be dephosphorylated preferentially except the domain responsible for the catalytic activity and then dephosphorylated at catalytic domain by phosphatase.