De Novo Maltotriose Biosynthesis from the Reducing End by Spinacia oleracea L. Chloroplasts

Abstract

The distribution of 14C in the various glucose residues of maltotriose was studied as a function of time of photosynthesis of isolated chloroplasts of spinach (Spilnacia oeraca L.) using 4C02. The distribution of label showed that the reducing-end glucose residue was labeled first and the label subsequently distributed to the second and third glucose residues at approximately equal rates.A mechanism for the distribution of label and the synthesis of maltotriose from the reducing end is presented. The mechanism has postulated to be the same as that for the maltose synthase recently described by Schilling. Maltose biosynthesis from a-D-glucose-l-phosphate was characterized as involving two glucosyl intermediates by a double displacement mechanism with inversion of configuration. The mode of enzymic action by which maltosyl intermediates were transferred to glucosyl intermediates was consistent with the fractional distribution of radioactivity found in each glucose unit of maltotriose during short term photosynthesis experiments.Maltodextrins have not been generally recognized as constituents of photosynthetic tissue. Indeed, the maltodextrins were not observed as such until green algae were labeled during photosynthesis in '4C02. Following photosynthesis of Chlorella and Scenedesmus in "4C02 and extraction of these tissues, Bassham and Calvin (2) prepared radioautograms of two-dimensional chromatograms of the extracts. The radioautograms showed a homologous series of compounds extending from the origin to sucrose. The homologous series was identified by French (6) as maltodextrins (i.e. a-l,4-linked D-glucose oligosaccharides). Kandler (12) also observed the maltodextrin series on two-dimensional chromatograms ofvarious plant extracts following "'CO2 photosynthesis. Heber (9) reported tri-, tetra-, and pentasaccharides present in chloroplasts of Nitella, Valonia, and Chara. Maltotriose and maltotetraose represented a major percentage of the excretion products of Oscillatoria redeker (11). Jensen also noted maltodextrins in extracts of isolated spinach chloroplasts after photosynthesis in "'CO2 (10).Maltose biosynthesis in vivo has been shown to involve aglucose-I-P (18). A maltose synthase isolated from spinach was recently described by Schilling (19) from aG-I-P2 was shown to involve two glucosyl-enzyme intermediates (,BG-E and ,BG-E') by a double displacement mechanism:2 aG-l-P + E + E' .,BfG-E + ,BG-E' + 2 Pi ,BG-E + ,BG-E' = aG-f#G-E' + E aG-,BG-E' = aG-aG + E'(1) (2) (3) Robyt (17) has described a similar mechanism for polysaccharide biosynthesis involving transfer of activated monomer units to the reducing end of a growing polysaccharide chain covalently linked to the active site of the enzyme.The work reported in this paper describes the relationship of the above enzymic activity to a possible route of maltotriose biosynthesis. The labeling of maltotriose during photosynthesis in '4CO2 has been found to originate in the reducing end glucose moiety, and can be explained by extension of the glucosyl...

Lipotubuloids in ovary epidermis of Ornithogalum umbellatum act as metabolons: suggestion of the name ‘lipotubuloid metabolon’

“…Examination of photosynthesis in Arabidopsis with radioactive CO 2 revealed that the photosynthetic complex functions as a metabolon (Szecowka et al, 2013). Similar complexes have been identified in spinach chloroplasts (Linden and Schilling 1984) and in sunflower (Ito and Mitsumori 1992), and tobacco (Hasunuma et al, 2010) leaves.…”

Metabolic Fluxes in an Illuminated Arabidopsis Rosette

“…Mutagenesis of AGPase to promote in vivo activity led to an increase in maltose levels in the light (Hädrich et al, 2012). 14 CO 2 labeling studies of spinach chloroplasts detected very-short-term labeling of maltose from 14 CO 2 (Linden et al, 1975;Schilling, 1982;Linden and Schilling, 1984). As this molecule was asymmetrically labeled, its formation cannot be attributed to the action of b-amylase on starch.…”