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Substrate Activation of β-(1 → 3) Glucan Synthetase and Its Effect on the Structure of β-Glucan Obtained from UDP-D-Glucose and Particulate Enzyme of Oat Coleoptiles
C. M. Tsai and W. Z. Hassid
Vol. 51, No. 6 (Jun., 1973), pp. 998-1001
Published by: American Society of Plant Biologists (ASPB)
Stable URL: http://www.jstor.org/stable/4263259
Page Count: 4
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UDP-D-glucose, at a micromolar level in the presence of MgCl2 and oat (Avena sativa) coleoptile particulate enzyme which contains both β-(1 → 3) and β-(1 → 4) glucan synthetases, produces glucan with mainly β-(1 → 4) glucosyl linkages. An activation of β-(1 → 3) glucan synthetase by UDP-D-glucose and a decrease in the formation of β-(1 → 3) glucan in the presence of MgCl2 have been observed. However, at high substrate concentration (≥ 10-4 M), the activation of β-(1 → 3) glucan synthetase is so pronounced that the formation of β-(1 → 3) glucosyl linkage predominates in synthesized glucan regardless of the presence of MgCl2. These observations may explain the striking shift in the composition of glucan of particulate enzyme from a β-(1 → 4) to β-(1 → 3) glucosyl linkage when UDP-D-glucose concentration is raised from a low concentration (≤ 10-5 M) to a higher concentration (≥ 10-4 M). Besides UDP-D-glucose, CDP-D-glucose can also serve as substrate for the formation of β-(1 → 3) glucan in the presence of β-(1 → 3) synthetase.
Plant Physiology © 1973 American Society of Plant Biologists (ASPB)