I. S. Bhatia

Studies on fructosyl transferase from Agave americana

Abstract The possible role of fructosyl transferase in the biosynthesis of fructosans in Agave americana was investigated. This enzyme was extracted from A. americana stem and purified 17.5-fold by salt fractionation and DEAE-cellulose chromatography. The optimum conditions for the enzyme were pH 6. 1, temperature 37°, substrate concentration 20% and Km 3.6 × 10−1 M; Ag+, Pb 2+, Hg2+, Al3+, Sn2+, CN− acted as inhibitors and Ca2+, Mg2+, Co2+ and Li+ actemd as activators. Only sugars of the type F ∼ R (R-aidose), e.g. sucrose and raffinose acted as substrates for the enzyme. The donor acceptor specificity of the enzyme was studied extensively. Sugars sucrose. None of the intermediates of fructosan biosynthesis from sucrpse acted as fructose donors. The possible acceptors from sucrose and raffinose. The enzyme was capable of building up oligosaccharides up to FIOG from sucrose. None of the intermediates of fructosan biosynthesis from sucrose acted as fructose donors. The possible mechanism of fructosan biosynthesis from sucrose is discussed.

Glucofructosan biosynthesis in Fusarium oxysporum

Abstract Low MW glucofructosans have been detected in the medium of Fusarium oxysporum . A 53-fold purification of fructosyl transferase has been achieved by ethanol precipitation, DEAE-cellulose and Sephadex G-100 column chromatography. Maximum fructosyl transferase activity coincided with maximum glucofructosan concentration in the medium. Invertase showed greatest activity in the later stages of growth when glucofructosans were absent. Fructosyl transferase and invertase have been separated by DEAE-cellulose column chromatography. On the basis of kinetic studies and effect of nucleotides on fructosyl transferase in the presence and absence of MgCl 2 , a two site active centre linked through a nucleotide bridge is proposed. Fructosyl transferase and invertase are highly phosphorylated.

Glucofructosan biosynthesis in Fusarium oxysporum: Regulation and substrate specificity of fructosyl transferase and invertase

Abstract Mycelium of Fusarium oxysporum grown on a glucose-containing medium lacked fructosyl transferase and invertase activities. Synthesis of fructosyl t

Isolation and characterization of fructosyltransferase from chicory roots

Abstract The occurrence of fructosyltransferase was demonstrated in the roots of chicory. The enzyme was purified 14-fold by ammonium sulphate fractionation and sephadex column chromatography. The optimal conditions for activity were pH 5·6, 37° and substrate (sucrose) concentration of 5·84 × 10 −1 M. The K m of the enzyme was found to be 2·85 × 10 −1 M. The enzyme was completely inactivated at 62·5°. Neither dialysis nor addition of inorganic phosphate affected its activity. The enzyme was capable of synthesizing glucofructosans from sucrose alone with the simultaneous release of glucose until seven oligosaccharides were synthesized, and with progressive enzyme activity small quantities of fructose were also released. Ag + and Hg 2+ completely inhibited the enzyme action, whereas, Cu 2+ , Zn 2+ , Fe 2+ , Na + , K + and Ca 2+ had almost no effect. The enzyme activity was significantly increased by Mn 2+ , Mg 2+ , Co 2+ and Ni 2+ .

Lipid biosynthesis in developing kernels of almond (Prunus amygdalus)

Abstract An active process of oil filling which was initiated at 50 DAF (days after fertilization) reached a maximum level at 70 DAF, as revealed by [1-14C]acetate incorporation into lipids of developing almond kernels. A several-fold incorporation into total lipids was recorded with [1-14C]acetate, compared with [U-14C]glucose. Labelled glucose was incorporated mainly into the polar lipid fraction. Glycolipids were more effectively synthesized with [U-14C]glucose than with [1-14C]acetate with a partial loss of label in phosphatidylinositol (PI) and diphosphatidylglycerol (DPG) fractions. Addition of 0.5 mM glucose and glycerol, either singly or in combination, enhanced [1-14C]acetate incorporation into lipids at 50 DAF while at 70 DAF these compounds decreased the label. The possible role of cofactors like NADPH and/or ATP and glycerol originating from glucose has been discussed.

Glucofructosan metabolism in Cichorium intybus roots

Abstract A 10-fold purification of sucrose sucrose fructosyl transferase from Cichorium intybus roots was achieved by ammonium sulphate fractionation and DEAE-cellulose column chromatography. The energy of activation for this enzyme was ca 48 kJ/mol sucrose. Sucrose sucrose fructosyl transferase and invertase were prominent during early months of growth. Evidence obtained from: (1) the changes in carbohydrate composition at monthly intervals; (2) comparative studies on fructosyl transferase and invertase at different stages of root growth; and (3) incubation studies with [ 14 C]glucose, [ 14 C]fructose and [ 14 C]sucrose revealed that, during the later stages of root growth, fructosan hydrolase is responsible for fructosan hydrolysis. No evidence for the direct transfer of fructose from sucrose to high M r glucofructosans was obtained.

Substrate specificity of fructosyl transferase from chicory roots

Abstract The substrate specificity of the enzyme, fructosyl transferase (sucrose-sucrose 1-fructosyl transferase) from chicory root was studied by incubating a number of sugars, alone and in combination, with the enzyme. Sucrose was found to be the true substrate. The oligosaccharide synthesized from sucrose was identified as the trisaccharide 1 F -fructosyl sucrose.

Interconversion of Free Sugars, Starch and the activity of Invertase and Sucrose-UDP (ADP) Glucosyl Transferase in the Storage Organ of a Pennisetum hsybrid

Summary Changes in free sugars, starch and the activity of invertase, sucrose-UDP glucosyl transferase and sucrose-ADP glucosyl transferase were studied in the storage organs of Pennisetum (Napier-Pearl millet) hybrid NB21 during continuous and intermittent growth (cuttings) of the plant. The relative level of reducing sugars decreased with a concomitant increase in the level of non-reducing sugars during continuous growth of the plant. During intermittent growth, the total free sugar levels decreased in alternate cuttings with the corresponding increase in the level of starch. The levels of sucrose-UDP glucosyl transferase, sucrose-ADP glucosyl transferase and sucrose increased in this organ with the growth of the plant. Sucrose was converted to starch through the intermediate formation of UDP-glucose and ADP-glucose. The activity of sucrose- UDP-glucosyl transferase was much higher than sucrose ADP-glucosyl transferase. Invertase catalyzed the utilization of sucrose for both respiration and starch synthesis at the initial stages of plant growth. At subsequent stages of plant growth, sucrose-UDP glucosyl transferase and sucrose-ADP glucosyl transferase became the major enzymes in the conversion of sucrose to starch. Starch of the storage organ is probably utilized in sprouting and fresh growth following cutting of the plant. Some oligomers, other than sucrose, are synthesized transitionally in the storage organ which are reused for regrowth of the plant.

Polar Lipid Composition During Sunflower (Helianthus annuus) Seed Development

Summary The changes in the total lipids, polar lipids and their fatty acid composition at different stages of maturity of sunflower seed were studied. There was a rapid synthesis of oil between 10–30 days after fertilization and the synthesis reached its peak between 20–30 days after fertilization. The amount of polar lipids increased slowly as compared to non-polar lipids throughout the ripening period. Fatty acid composition of maturing seeds indicated a de novo synthesis of fatty acids along with the oil up to 30 days after fertilization and thereafter the desaturation process perhaps became active. Marked changes were observed in the fatty acid composition of individual polar lipid components during development. Among the phosphatides the fatty acid composition of PA and DPG resembled at all stages of development, thereby indicating some biosynthetic relationship between the two phosphatides.

Polar lipids of sun flower (Helianthus annuus L.) seeds

Qualitative and quantitative analysis of polar lipids in sun flower (Helianthus annuus L.) seed is reported in the present study. Ten classes of polar lipids i.e. phosphatidic acid, phosphatidyl inositol, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl glycerol, diphosphatidyl glycerol, digalactosyl diglyceride, monogalactosyl diglyceride, esterified sterol glycoside and free fatty acids have been identified. Phosphatidyl choline and phosphatidyl inositol formed the major phosphatide fractions. Only four fatty acids i.e. palmitic, stearic, oleic and linoleic acids were present in measurable amounts in the total polar lipids. There was a great variation in the fatty acid composition in different classes of polar lipids. Arachidic acid was present in all the individual phosphatide fractions. Phosphatidyl glycerol was highly unsaturated followed by esterified sterolglycoside, phosphatidic acid, phosphatidyl ethanolamine + phosphatidyl glycerol, diphosphatidyl glycerol and monogalactosyl diglyceride.