Phytases catalyse the hydrolytic degradation of phytic acid and its salts and are added to monogastric animal feed to ameliorate the negative environmental and nutritional consequences of dietary phytate. Screening of 58 microbial strains identified a phytase produced by Rhizopus oligosporus ATCC 22959 that displayed physicochemical characteristics likely to render it of potential industrial interest. The 124 kDa enzyme was purified to homogeneity by anion exchange chromatography, gel filtration and chromatofocusing. The monomeric glycosylated enzyme (30.5% total carbohydrate) displayed maximum activity at 65 degreesC and pH 5.0. It displayed a K-m of 10.4 muM, a V-max of 1.32 nmol s(-1) and a K-cat of 51 s(-1). It is acid tolerant, retaining full activity after incubation at pH 2.0 for 6 h. HPLC analysis indicated the enzyme's ability to almost completely degrade phytate. Substrate specificity studies showed its ability to dephosphorylate several additional phosphorylated molecules. Activity was unaffected or moderately stimulated by a range of metal ions with only Ca2+ exerting a modest (13%) inhibitory effect. The enzyme is significantly more thermostable at 80 degreesC and retains a significantly greater proportion of maximal activity at physiological temperatures than do two commercial phytases tested for comparative purposes. This may render it of industrial interest. (C) 2004 Elsevier B.V. All rights reserved.