Chloroplasts from 5 to 7 day old Vigna radiata seedling, grown under alternate light/dark conditions or from green Eugkna gracilis Z. cells have been found to harbor L-myo-inositol-l-phosphate synthase (EC 5.5.1.4) activity. In contrast, dark-rown V. radiata seedlings, or streptomycin-bleached Eugkna cells exhibit either reduced or no enzyme activity. An apparent enhancement of the chloroplastic inositol synthase by growth in presence of light is observed.An irreversible NAD-dependent oxidation-reduction reaction brings about the cyclization of glucose 6-P (G-6-P) to myoinositol 1-P. The enzyme catalyzing this reaction, L-myo-inositol 1-P synthase (EC 5.5.1.4, hitherto referred to as synthase) has been reported from a number of eukaryotic sources (18). In each case, the activity was isolated as constituent of the soluble cytosolic fraction of the cell preparation.In the green plant chloroplast, about 10% of the membrane phospholipids consist of phosphoinositides (17)

1984. L-Myo-inositol-1-phosphate synthase from lower plant groups: Partial purifieation and properties of the enzyme from Euglena gracilis. -Physiol. Plant. 61: 412-416.A survey for the enzyme i,-myo-inositol-l-phosphate synthase (EC 5.5.1.4) has been conducted among various members of the lower plant groups, mainly algae, bryophytes and fungi; some properties of the partially purified enzyme from Euglena gracilis Z. are presented. The enzyme was detected in Chlorophycean algae, Marehantiales and the Basidiomyeetous fungi. The enzyme from Ettgleita had a pH optimum at 7.5. The Km for glucose-6-P was 2.1 mM and for NAD+ 80 \iM. When assayed in the absenee of added NAD+, the enzyme showed a basal activity suggesting the presence of bound NAD+ in the system. NHjCI increased the enzyme activity two-fold, although the enzyme was inactivated by (NH)SOAdditional key words -Inositol synthase, myo-inositol.

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L‐myo‐inositol‐1‐phosphate synthase (EC 5.5.1.4) from mammalian fetal and adult brain differ considerably with respect to their stability towards different temperatures between 25–65°C. This property has been found to be associated with the presence of the synthase co‐factor, NAD, bound to the enzyme protein. The lower thermal stability of the fetal enzyme increases in presence of added NAD (0.8 mM) whereas the higher thermal stability of the adult brain enzyme declines when NAD is specifically removed from the enzyme.

Myo-inositol is involved in normal growth and development of all living organisms and L-myo-inositol-1-phosphate synthase (MIPS; EC: 5.5.1.4) is responsible for its de novo synthesis. This enzyme has been reported for a number of life forms including plants, animals and bacteria. In the present study free myo-inositol has been detected in the common pteridophytes found in the Darjeeling Himalayas and the enzyme, L-myo-inositol-1-phosphate synthase has been partially purified from Diplopterygium glaucum (Thunb.) Nakai. A crude homogenate from the reproductive pinnules of D. glaucum was subjected to streptomycin sulphate precipitation and 0-70% ammonium sulphate fractionation followed by successive chromatography through DEAEcellulose, Hexylagarose and BioGel A-0.5m columns. This resulted in a partial purification of the enzyme of about 81-fold with 13.5% recovery. The pteridophytic MIPS specifically utilized D-glucose-6-phosphte and NAD + as its substrate and co-factor, respectively. It shows a pH optimum between 7.0 and 7.5 while the temperature maximum was 30 °C. The enzyme activity was stimulated by NH 4 + , slightly inhibited by Na + , Ba 2+ and Cd 2+ , and strongly inhibited by Li + , Zn 2+ and Hg 2+ . EDTA, pCMB and some substrate isomers like glucose-1-phosphate, fructose-6-phosphte and galactose-6-phosphate were inhibitory to the enzyme. The apparent molecular weight of the native D. glaucum MIPS was determined to be approximately 171 kDa. Key words: D-glucose-6-phosphate, Gleicheniaceae, inositol synthase, myo-inositol. Conteúdo de myo-inositol em pteridófitas e o isolamento e caracterização da sintase de L-myo-inositol-1-fosfato de Diplopterygium glaucum:Myo-inositol está envolvido no crescimento e desenvolvimento de todos os organismos vivos e a enzima sintase do L-myo-inositol-1-fosfato (MIPS; EC: 5.5.1.4) é responsável pela sua síntese de novo. Esta enzima tem sido relatada em um número grande de plantas, animais e bactérias. No presente estudo myo-inositol não complexado foi detectado em pteridófitas comuns encontradas em Darjeeling Himalayas e a enzima sintase do L-myo-inositol-1-fosfato foi parcialmente purificada a partir de Diplopterygium glaucum (Thunb.) Nakai. Um extrato protéico não purificado de pinulas reprodutivas foi precipitada com sulfato de estreptomicina e 0-70% sulfato de amônia seguido de sucessivas cromatografias em colunas de DEAE-celulose, Hexylagarose e BioGel A. Este procedimento resultou na purificação parcial de 81 vezes, com recuperação de 13.5%. A MIPS dessa pteridófita usou especificamente D-glicose-6-fosfato and NAD + como substrato e cofator, respectivamente. Mostrou pH ótimo entre 7,0 e 7,5, enquanto a temperatura ótima foi 30°C. A atividade da enzima foi estimulada por NH 4 + , pouco inibida por Na + , Ba 2+ e Cd 2+ , e fortemente inibida por Li + , Zn 2+ e Hg 2+ . EDTA, pCMB e alguns substratos isôme-ros, como glicose-1-fosfato, frutose-6-fosfato e galactose-6-fosfato inibiram a enzima. A massa molecular aparente da MIPS de D. glaucum é aproximadamente 171 kDa. Palavr...