FIG. 4.

Effect of rabbit polyclonal antiserum on UMP kinase activity. (A) UMP kinase (0.035 U, corresponding to 0.5 μg of protein) in 100 μl of PBS was incubated for 15 min with various amounts of polyclonal anti-UMP kinase antiserum as indicated on the abscissa, and then the residual activity was measured as described in Materials and Methods, with 1 mM ATP and 0.3 mM UMP as substrates (•). Equivalent volumes of unrelated rabbit polyclonal antiserum (■) were used as a control. (B) Antiserum at a concentration calculated to achieve 70% inhibition of enzymatic activity was incubated in 40 μl with fragment 1-180 in the indicated amounts. UMP kinase (0.04 U, corresponding to 0.7 μg of protein) was then added to this mixture, and after 1 min of incubation, the residual activity was measured with 1 mM ATP and 0.3 mM UTP as substrates. One hundred percent represents the UMP kinase activity that would be obtained in the absence of both the polyclonal antiserum and fragment 1-180.