Showing papers by "Frank A. Loewus published in 1982"
TL;DR: Myo-Inositol-1-phosphatase links myo-inositol biosynthesis to themyo- inositol oxidation pathway to produce an alternative path from d-glucose 6-ph phosphate to UDP-d- glucuronate that bypasses UDP- d-Glucose dehydrogenase.
Abstract: A Mg 2+ -dependent, alkaline phosphatase has been isolated from mature pollen of Lilium longiflorum Thunb., cv. Ace and partially purified. It hydrolyzes 1l- and 1d- myo -inositol 1-phosphate, myo -inositol 2-phosphate, and β-glycerophosphate at rates decreasing in the order named. The affinity of the enzyme for 1l- and 1d- myo -inositol 1-phosphate is approximately 10-fold greater than its affinity for myo -inositol 2-phosphate. Little or no activity is found with phytate, d-glucose 6-phosphate, d-glucose 1-phosphate, d-fructose 1-phosphate, d-fructose 6-phosphate, d-mannose 6-phosphate, or p -nitrophenyl phosphate. 3-Phosphosphoglycerate is a weak competitive inhibitor. myo -Inositol does not inhibit the reaction. Optimal activity is obtained at pH 8.5 and requires the presence of Mg 2+ . At 4 millimolar, Co 2+ , Fe 2+ or Mn 2+ are less effective. Substantial inhibition is obtained with 0.25 molar Li + . With β-glycerophosphate as substrate the K m is 0.06 millimolar and the reaction remains linear at least 2 hours. In 0.1 molar Tris, β-glycerophosphate yields equivalent amounts of glycerol and inorganic phosphate, evidence that transphosphorylation does not occur. In higher plants this myo -inositol-1-phosphatase links myo -inositol biosynthesis to the myo -inositol oxidation pathway to produce an alternative path from d-glucose 6-phosphate to UDP-d-glucuronate that bypasses UDP-d-glucose dehydrogenase. myo -Inositol-1-phosphatase also furnishes free myo -inositol for reactions that lead to other cyclitols and cyclitol-containing compounds of biosynthetic and/or regulatory significance in plant growth and development.
46 citations
TL;DR: Ochromonas danica Pringsheim, a freshwater chrysomonad, converts d-glucose into l-ascorbic acid over a metabolic pathway that inverts the carbon chain of the sugar, and resembles that found in ascorbic acid-synthesizing animals.
Abstract: Ochromonas danica Pringsheim, a freshwater chrysomonad, converts d-glucose into l-ascorbic acid over a metabolic pathway that `inverts9 the carbon chain of the sugar. In this respect, l-ascorbic acid formation resembles that found in ascorbic acid-synthesizing animals. It differs from this process in that d-galacturonate and l-galactono-1,4-lactone, rather than d-glucuronate and l-gulono-1,4-lactone, enhance production of ascorbic acid and repress the incorporation of 14 C from d-[1- 14 C]glucose into ascorbic acid.
44 citations
TL;DR: Results are consistent with the formation of l-threonate from carbons three through six of l -ascorbic acid and suggest a process involving decarboxylation of l-[U-(14)C]threonates.
Abstract: l-Threonic acid is a natural constituent in leaves of Pelargonium crispum (L.) L9Her (lemon geranium) and Rumex x acutus L. (sorrel). In both species, l-[ 14 C]threonate is formed after feeding l-[U- 14 C]ascorbic acid to detached leaves. R. acutus leaves labeled with l-[4- 3 H]- or l-[6- 3 H]ascorbic acid produce l-[ 3 H]threonate, in the first case internally labeled and in the second case confined to the hydroxymethyl group. These results are consistent with the formation of l-threonate from carbons three through six of l-ascorbic acid. Detached leaves of P. crispum oxidize l-[U- 14 C] threonate to l-[ 14 C]tartrate whereas leaves of R. acutus produce negligible tartrate and the bulk of the 14 C appears in 14 CO 2 , [ 14 C]sucrose, and other products of carbohydrate metabolism. R. acutus leaves that are labeled with l-[U- 14 C]threonate release 14 CO 2 at linear rate until a limiting value of 25% of the total [U- 14 C]threonate is metabolized. A small quantity of [ 14 C]glycerate is also produced which suggests a process involving decarboxylation of l-[U- 14 C]threonate.
43 citations
TL;DR: The product of myo-inositol-1-phosphate synthase, EC 5.5.1.4, from mature pollen of Lilium longiflorum Thunb.
Abstract: The product of myo-inositol-1-phosphate synthase, EC 5.5.1.4, from mature pollen of Lilium longiflorum Thunb., cv Ace (Easter lily) and that of myo-inositol kinase, EC 2.7.1.64, from wheat germ has been identified as 1l-myo-inositol-1-phosphate by gas chromatography of its trimethylsilyl-methyl phosphate derivative on a glass capillary column bearing a chiral phase.
31 citations
TL;DR: The fate of phytate-derived myo-inositol during germination of wheat is discussed in relation to a recent scheme ofphytate metabolism proposed by De and Biswas for germinating mung bean seedlings.
Abstract: Wheat kernels from myo -[2- 3 H]inositol- or scyllo -[ R - 3 H]inositol-labeled plants (Sasaki and Loewus 1980 Plant Physiol 66: 740-745) were used to study redistribution of 3 H into growing regions during germination. Most of the labeled 1-α-galactinol (or the analogous scyllo -inositol galactoside) was hydrolyzed within 1 day. Water-soluble phytate was dephosphorylated within 3 days. A large reserve of bound phytate continued to release myo -inositol over several days. Translocation of free myo -inositol to growing regions provided substrate for the myo -inositol oxidation pathway and incorporation of 3 H into new cell wall polysaccharides. Cell wall polysaccharides in the kernel were degraded during germination. The labeled residues were translocated to growing regions and reutilized for new cell wall formation. Pentosyl residues accounted for most of this label. Free scyllo -inositol followed a path of translocation from kernel to seedling similar to that of myo -inositol. Unlike myo -inositol, it did not furnish substrate for the myo -inositol oxidation pathway but accumulated as free scyllo -inositol in the seedling. The fate of phytate-derived myo -inositol during germination of wheat is discussed in relation to a recent scheme of phytate metabolism proposed by De and Biswas (1979 J Biol Chem 254: 8717-8719) for germinating mung bean seedlings.
11 citations
TL;DR: Results indicate that during l-ascorbic acid biosynthesis from glucose in Pelargonium crispum hydrogen at carbon 5 undergoes exchange with the medium, suggesting an epimerization at this carbon atom.
Abstract: Conversion of d-[5- 3 H,6- 14 C]glucose to l-ascorbic acid in detached apices of Pelargonium crispum (L.) L9Her cv Prince Rupert (lemon geranium) was accompanied by complete loss of tritium in the product. Chemical degradation of d-glucose which was recovered from the labeled apices yielded d-glyceric acid (corresponding to carbons 4, 5, and 6 of glucose) with a 3 H: 14 C ratio of 4 to be compared with 9, the ratio in d-[5- 3 H,6- 14 C]glucose initially. Conversion of d-[6- 3 H,6- 14 C]glucose in the same tissue was accompanied by retention of tritium in l-ascorbic acid with a 3 H: 14 C ratio comparable to that of compounds from the hexose pool. Results indicate that during l-ascorbic acid biosynthesis from glucose in Pelargonium crispum hydrogen at carbon 5 undergoes exchange with the medium, suggesting an epimerization at this carbon atom.
11 citations