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Articles

Factors Influencing -Glucan Synthesis by Particulate Enzymes from Suspension-Cultured Lolium multiflorum Endosperm Cells ¹

Department of Biochemistry, La Trobe University, Bundoora, Victoria 3083, Australia

Particulate enzymes from suspension-cultured ryegrass (Lolium multiflorum Lam.) endosperm cells incorporated glucosyl residues from UDP-glucose and GDP-glucose into -glucans. Three types of -glucans were produced from UDP-glucose: 1,3--glucan; 1,4--glucan; and mixed-linkage 1,3;1,4--glucan. As in other systems, relatively more 1,4--glucan was produced from a low (10 micromolar) UDP-glucose concentration, and relatively more 1,3--glucan was produced from a high (1 millimolar) UDP-glucose concentration. However, in ryegrass, 1,3;1,4--glucan represented a major proportion of the products at both low and high UDP-glucose concentrations. The arrangement of linkages in the 1,3;1,4--glucan was different at the two concentrations; at the low UDP-glucose concentration, more sequences of three consecutive 1,4-linkages were produced.

The effects of pH, temperature, and metal ion concentrations on incorporation were dependent on the UDP-glucose concentration. At the low UDP-glucose concentration, incorporation into all three types of -glucan increased with increasing pH. At the high UDP-glucose concentration, 1,3--glucan was the major product at pH 7 and below; 1,4--glucan synthesis was optimal at pH 8; and synthesis of 1,3;1,4--glucan was greatest above pH 8.

With 10 micromolar GDP-glucose as substrate, 1,4--glucan, but no 1,3;1,4--glucan, was produced. Incorporation from either UDP-glucose or GDP-glucose was not influenced by the presence of the other.

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