Interaction of Porcine Uterine Fluid Purple Acid Phosphatase with Vanadate and Vanadyl Cation

Debbie C. Carans, Colorado State University - Fort Collins
Carmen M. Simone, Colorado State University - Fort Collins
Richard C. Holz, Marquette University
Lawrence Que,Jr, University of Minnesota - Twin Cities

Biochemistry, Vol. 31, No. 47 (December 1992): 11740-11747. DOI.

Richard Holz was affiliated with University of Minnesota at the time of publication.


Uteroferrin, the purple acid phosphatase from porcine uterine fluid, is noncompetitively inhibited by vanadate in a time-dependent manner under both aerobic and anaerobic conditions. This time-dependent inhibition is observed only with the diiron enzyme and is absent when the FeZn enzyme is used. The observations are attributed to the sequential formation of two uteroferrin-vanadium complexes. The first complex forms rapidly and reversibly, while the second complex forms slowly and results in the production of catalytically inactive oxidized uteroferrin and V(IV), which is observed by EPR. The redox reaction can be reversed by treatment of the oxidized enzyme first with (V(1V)) and then EDTA to generate a catalytically active uteroferrin. Multiple inhibition kinetics suggests that vanadate is mutually exclusive with molybdate, tungstate, and vanadyl cation. The binding site for each of these anions is distinct from the site to which the competitive inhibitors phosphate and arsenate bind. The time-dependent inhibition by vanadate of uteroferrin containing the diiron core represents a new type of mechanism by which vanadium can interact with proteins and gives additional insight into the binding of anions to uteroferrin.