Braz. J. Plant Physiol., 19(2):109-117, 2007 RESEARCH ARTICLE Occurrence of myo-inositol-1-phosphate phosphatase in pteridophytes: characteristics of the enzyme from the reproductive pinnules of Dryopteris filix-mas (L.) Schott Ritwika Banerjee 1 , Dhani R. Chhetri 2 and Jukta Adhikari 1 * 1 Post-Graduate Department of Botany, Presidency College, 86/1 College Street, Kolkata  700073, India. 2 Post-Graduate Department of Botany, Darjeeling Govt. College, Darjeeling  743101, India. *Corresponding author: adhikarijukta@gmail.com Received: 04 April 2007; Returned for revision: 02 July 2007; Accepted: 30 July 2007 Evident myo-inositol-1-phosphate phosphatase (MIPP) activity has been detected both in the vegetative as well as in the spore-bearing organs of some selected pteridophytes having wide phylogenetic diversity. The basic characterization of this enzyme was carried out using the cosmopolitan fern Dryopteris filix-mas. The enzyme was partially purified from the cytosol fraction obtained from the reproductive pinnules of the plant to about 41-fold over the initial homogenate following low-speed centrifugation, streptomycin sulfate precipitation, 25-70% ammonium sulfate fractionation, CM Sephadex C-50 chromatography and finally gel-filtration on Ultrogel AcA 34. The apparent molecular weight of the native MIPP was estimated to be 94 kDa. The enzyme activity increased linearly with respect to protein concentration to about 150 µg and with respect to time up to 75 min. The temperature optimum was found at 40”C. However, the enzyme showed good activity over the temperature range of 30-50”C. This enzyme used D/L-myo-inositol- 1-phosphate as its principal substrate (95-100%), however, about 16% activity was recorded when D-myo-inositol-3- phosphate substituted as substrate. Furthermore, weak (3%) activity of this MIPP was observed with 2- glycerophosphate as substrate. The apparent K m for pteridophytic MIPP was 0.083 mM. The enzyme was functional in a narrow pH range of 7.5 to 8.5. The activity of this MIPP enzyme was remarkably inhibited by the presence of a monovalent cation, lithium, and even moderately so at a low concentration such as 1 mM. On the other hand, magnesium, a divalent cation, enhanced activity at least up to 10 mM. Calcium diminished MIPP activity at concentrations over 4 mM. Key words: Dryopteris filix-mas, myo-inositol-1-phosphate phosphatase, pteridophytes, reproductive pinnules OcorrŒncia da fosfatase do mio-inositol-1-fosfato em pteridfitas: caractersticas da enzima a partir de pnulas reprodutivas de Dryopteris filix-mas (L.) Schott: Tem-se detectado atividade da fosfatase do mio-inositol-1-fosfato (FMIF) tanto em rgªos vegetativos como em estruturas esporulantes de algumas pteridfitas com ampla diversidade filogenØtica. Neste estudo, procedeu-se  caracterizaªo bÆsica dessa enzima utilizando-se da pteridfita cosmopolita Dryopteris filix-mas . Aps centrifugaªo em baixa velocidade, precipitaªo com sulfato de estreptomicina, fracionamento com sulfato de amnio (25-70%), cromatografia em CM Sephadex C-50 e, finalmente, filtraªo gØlica em Ultrogel AcA 34, conseguiu-se uma purificaªo parcial da enzima (a partir da fraªo citosslica obtida de pnulas reprodutivas da planta) de cerca de 41 vezes em relaªo ao homogenato inicial. O peso molecular aparente da FMIF nativa foi estimado em 94 kDa. A atividade da enzima aumentou linearmente com relaªo ao conteœdo de protena (cerca de 150 µg) e com relaªo ao tempo (atØ 75 min). A temperatura tima foi de 40”C. Entretanto, a enzima exibiu atividade razoÆvel na faixa de temperatura entre 30 e 50”C. O D/L-mio-inositol-1-fosfato foi o principal substrato (95-100%) da enzima, porØm registrou-se uma atividade de cerca de 16% quando este composto foi substitudo pelo D-mio-inositol-3- fosfato. Ademais, observou-se fraca atividade (3%) da FMIF quando se utilizou o 2-glicerol-fosfato como substrato. O