[The effect of phospholipids on starch metabolism]. / Einfluß von Phospholipiden auf den Stärkemetabolismus.

The presence of phospholipids reduces the breakdown of amylose catalyzed by ß-amylase, phosphorylase and α-amylase. The activities of the ß-amylases of sweet potato (Ipomoea batatas) and barley (Hordeum vulgare L.) disminish to less than 10% of the activity in the control without the phospholipids. When the amylose was complexed with phospholipids the activity of the α-amylase of Bacillus subtilis was reduced to about 25% of the control value. A similar effect was observed for the amylases of Zea mays leaves. The phosphorylase effected almost no phosphorolysis of the complexed amylose, but starch synthesis from glucose-1-phosphate proceeded at a rate that was about 60% of that with pure amylose. The activity of the synthetase from bundle sheath cells of maize leaves was not influenced much by the presence of phospholipids, whereas the "branching enzyme" of maize endosperm did not produce any amylopectin from the complexed amylose. -These facts could explain the simultaneous deposition of amylose and amylopectin in the starch granules. Some of the newly formed glucan chains may be protected by formation of a complex with the phospholipids. This protected amylose can not undergo branching or breakdown, but it can be elongated owing to the activity of synthetase or phosphorylase. Amylopectin is formed from the chains that are not complexed.

[Sucrose metabolizing enzymes in roots]. / Enzyme des Saccharosestoffwechsels in Wurzeln.

In tomato, pea, and maize roots, the presence of sucrose synthetase (E.C. 2.4.1.13), sucrose phosphate synthetase (E.C. 2.4.1.14), and both the alkaline and acid sucrases (E.C. 3.2.1.? and E.C. 3.2.1.26) could be demonstrated. The activity of these enzymes was measured directly on root slices suspended in the incubation mixture, which also contained 10% dimethyl sulfoxide or 5% ethyl acetate. These two additives increase the permeability of the membranes, thus allowing the entry of substrates to the site where the enzymes are located and favouring the release of products into the medium. The values found by measuring the activities of sucrose synthetase and the alkaline sucrase on tomato root were quite comparable to those obtained using enzymic preparations of the same tissue. In the case of the weakly active sucrose phosphate synthetase and the very active acid sucrase, the comparison of the two methods showed that losses of activity occurred during the preparation of the enzymes. By separating stele from cortex in tomato and maize roots, it could be shown that sucrose phosphate synthetase is located only in the stele, while the other enzymes are unevenly distributed between the two tissues, the sucrases predominating in the cortex. Sucrose phosphate synthetase and sucrose synthetase are most active in the region with root hairs of maize roots, while the activity of both sucrases is higher in the region near the apex. The highest invertase activity was measured in the apex of stem-borne adventitious roots that had not yet penetrated the soil. In older roots, sucrose phosphate synthetase disappears and the activity of all the other enzymes diminishes. It is suggested that the high activity of sucrose synthetase is present in the regions where an active synthesis of cell wall substances from glycosyl nucleotides is taking place, while the sucrases provide the initial substrates for most of the other pathways.

[On the activity of synthetase and phosphorylase in maize leaves at different starch levels]. / Über die Aktivität der Synthetase und Phosphorylase in Maisblatt bei verschiedenen Stärkegehalten.

The activities of phosphorylase and synthetase in the bundle sheath cells of maize leaves were investigated in plants that as a result of different light-dark treatments contained various amounts of starch. The material coming from the dark (67 h) had almost no starch and scarcely any synthetase activity if starch granules were not added to the assay mixture as a primer. In the presence of this primer a poor synthetase activity could be detected. After 2 h in the light the leaves produced a small amount of starch and the synthetase activity increased. When starch granules were included in the test the synthetase activity was increased 3.5-fold. This value was 1.5-fold higher than the corresponding one in the dark. Plants that were in the light for 28 h contained fair amounts of starch and the synthetase activity was independent of the addition of primer. The values were 3 fold higher than those found in plants in the dark. A further increase in the synthetase activity and decrease in starch content were brought about by a dark period of 2 h following the illumination of 28 h.The total activity of phosphorylase remained high and almost constant in all these materials and did not require the addition of primer to attain a maximal value. In the material coming from the dark, the product produced by the activity of phosphorylase in absence of added primer could serve as a good primer for the synthetase. From the comparison of the amounts of starch produced in vivo under different conditions and the enzymic activities found we conclude that the first steps of starch synthesis are carried out by phosphorylase and that further on both enzymes participate in the process.

[G-1-P as precursor for starch synthesis in bundle sheath cells of Zea mays]. / Die Bedeutung des Glucose-1-Phosphates für die Stärkesynthese in den Bündelscheidenzellen von Zea mays.

After illumination intact leaves of Zea mays contain sucrose and starch. The latter is located mainly in the bundle sheath cells. When 0.5 mm wide leaf strips are incubated with sucrose solution, the starch deposit in the bundle-sheath chloroplasts is greatly increased by light. When isolated bundle sheath cells are suspended in water or solutions of sucrose and various metabolites they are not capable of synthesizing starch. An appreciable production of starch in the chloroplasts of isolated bundle sheath cells can be observed only in the presence of glucose-1-phosphate.