datavaluefield dropdownlist

Question

i want to change dropdownlist 'datavaluefield' dynamically.

            protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
                 {
                      sle_1.Text = DropDownList1.SelectedValue.ToString();

                              DropDownList1.DataValueField = "company";
                       sle_2.Text = DropDownList1.SelectedValue.ToString();
                   }
i  have set the       dropdownlist1.datavaluefield="agent_name" in pageload.

                  am getting 'agent_name' in textbox 'sle1_1' and textbox 'sle_2'
but my requirement is afte 'sle_1.text' am trying to change datavaluefield i want to print 'company'  in sle_2

please help me