Multiple forms of -1,4 glucan synthetase from spinach leaves

Soluble starch synthases and starch branching enzymes from cotyledons of smooth- and wrinkled-seeded lines of Pisum sativum L

Soluble starch synthase and branching enzyme were purified from 18-day-old cotyledons of the smooth-seeded pea cultivar Alaska (RR) and wrinkled-seeded pea cultivar Progress #9 (rr) by DEAE-cellulose chromatography. Two coeluting peaks of primed and citrate-stimulated starch synthase activity and a major and minor peak of branching enzyme activity were observed in Alaska. However, in Progress #9, only one peak of synthase activity was found. When crude extracts of Progress #9 were centrifuged, over 70% of the starch synthase activity was recovered in the pelleted fraction, and additional washings of the pellet released no further activity. The addition of purified starch granules to Alaska crude extracts also resulted in the recovery of a greater proportion of synthase activity in pelleted fractions. The two peaks of branching enzyme activity in Alaska differed in their stimulation of phosphorylase, amylose branching activity, and activity in various buffers. The DEAE-cellulose profile of Progress #9 showed no distinct peak of branching enzyme and less than 10% of the total activity found in Alaska. The association of one form of soluble starch synthase with the pelleted fraction and the greatly reduced levels of branching enzyme provide a partial explanation for the appearance of high-amylose starch in Progress #9 cotyledons.

Primer dependent and independent forms of soluble starch synthetase from developing barley endosperms

The activity of soluble starch synthetase (ADP-glucose: α-1,4-glucan α-4-glucosyltransferase) in the non-purified extract from 16 day-old Bomi barley endosperms (Hordeum vulgare L.) was low and the reaction was non-linear when plotted against protein concentration. Starch synthetase was purified by ammonium sulfate precipitation and DEAE-cellulose chromatography and separated into four fractions. In the absence of an added carbohydrate primer two of the four fractions catalized the synthesis of a methanol-precipitable α-glucan when high concentrations of sodium citrate and bovine serum albumim were added. The rate of α-glucan synthesis by the unprimed reaction was higher than for the primed reaction. The four enzyme fractions were active with ADP-Glc, but not with UDP-Glc, both in the primed and in the unprimed reaction.

Location of enzymes metabolising sucrose and starch in the grasses Pennisetum purpureum and Muhlenbergia montana

Leaf tissue of the panicoid grass Pennisetum purpureum (Schum) and of the chloridoid grass Muhlenbergia montana (Hitchcock) were fractionated to produce preparations enriched in the contents of mesophyll and bundle sheath cells. Sucrose phosphate synthetase and sucrose synthetase were found predominantly in the mesophyll tissues of both species, as was uridine-diphosphate-glucose pyrophosphorylase in Pennisetum. In Muhlenbergia this enzyme was more plentiful in the bundle sheath cell fraction.Starch synthetase and adenosine-diphosphate-glucose pyrophosphorylase were plentiful in bundle sheath extracts of both species but phosphorylase was associated with extracts of mesophyll cells. In no case was there a clear-cut compartmentation of enzymes between leaf fractions.

Soluble adenosine diphosphate glucose- -1,4-glucan -4-glucosyltransferases from spinach leaves

Multiple forms of ADP-glucose-alpha-1,4-glucan alpha-4-glucosyltransferase were obtained from spinach leaves by gradient elution from a DEAE-cellulose column. In the presence of high concentrations of some salts and bovine serum albumin, unprimed activity was found in one (transglucosylase III) of the four fractions eluted from the column. In addition to having unprimed activity, transglucosylase III had a lower K(m) for ADP-glucose, a much higher K(m) for oyster glycogen, greater heat sensitivity and lower affinity for maltose, maltotriose and amylopectin beta-limit dextrin than fractions I, II and IV. In addition, the kinetics at low concentrations of amylose, amylopectin and rabbit liver glycogen were non-linear for transglucosylase III. The properties of transglucosylases I, II and IV were generally similar to each other. Rates of the unprimed reaction at physiological concentrations of ADP-glucose were greater than those found for the primed reaction of fraction III. The product formed by the unprimed reaction was a glucan containing principally alpha-1,4 linkages with some alpha-1,6 linkages. The primer, maltose, at a concentration of 0.5m inhibited the synthesis of the unprimed product.