Structure, Properties and Reactivity of the FeIIFeIII and ZnIIFeIII Purple Acid Phosphatases

Abstract

This microreview describes the structure, properties and mechanisms of the purple acid phosphatases (PAP). The enzyme is isolated from mammalian, plant and bacterial sources. X-ray structural information is now available for the enzyme from pig (uteroferrin), rat and kidney beans. Features of the mechanism are the concerted action of a labile MII centre (FeII or ZnII) alongside a more inert FeIII. The latter is effective as a conjugate-base FeOH2+, which initiates hydrolysis at the MII-bound phosphate ester by a process involving OH− replacement of OR− at the PV. Histidine residues near to the active site help bind the phosphate and are involved in the release of OR−. Effects of replacement of the FeII by MnII, CoII, NiII, CuII and ZnII, and of FeIII by GaIII,AlIII and InIII have been studied. The mechanistic role of the ZnIIZnII combination in alkaline phosphatases, and other related dinuclear centres is also considered.