Urate Oxidase and its Association with Peroxisomes in <i>Acanthamoeba</i> sp.

Abstract

Urate oxidase is present in axenic Acanthamoeba sp. (Neff strain). The enzyme shows an absolute requirement for molecular oxygen as electron acceptor and forms hydrogen peroxide. Its optimum of activity in 0.1 M Tris‐glycine buffer is at pH 9.4 with an apparent K m value of 18.7 μM. Its activity is inhibited by oxypurines, trichloropurine, oxonate and potassium cyanide. In all these properties the enzyme strongly resembles mammalian urate oxidases. Isopycnic centrifugation of Acanthamoeba homogenates in sucrose gradients showed that the distribution pattern of urate oxidase is identical with that of catalase but is different from the distribution of succinate dehydrogenase (a marker enzyme for mitochondria) and of acid phosphatase (a marker enzyme for lysosomes). The results strongly suggest the existence of a particle population with characteristics of peroxisomes in Acanthamoeba .