Properties of a purple phosphatase from red kidney bean: a zinc-iron metalloenzyme

A purple phosphatase from the red kidney bean Phaseolus vulgaris has been purified to homogeneity and characterized. It resembles sweet potato purple acid phosphatase in being a dimer of approx. 130 kDa and in its amino acid composition and visible absorption spectrum. The red kidney bean enzyme contains one atom of iron and one atom of zinc per subunit, whereas the sweet potato enzyme is reported to contain manganese. The visible absorption spectrum shows a λmax at 560 nm with ε{lunate}560 (per iron) = 3360 M- · cm-1, and is destroyed by dithionite treatment. Red kidney bean phosphatase shows a marked preference for ATP as substrate over p-nitrophenyl phosphate and ADP. Stable esters such as AMP and β-glycerophosphate are very poor substrates. The enzyme is compared with other purple phosphatases from plant and animal sources