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

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Abstract
Particulate enzymes from suspension-cultured ryegrass (Lolium multiflorum Lam.) endosperm cells incorporated glucosyl residues from UDP-glucose and GDP-glucose into β-glucans. Three types of β-glucans were produced from UDP-glucose: 1,3-β-glucan; 1,4-β-glucan; and mixed-linkage 1,3;1,4-β-glucan. As in other systems, relatively more 1,4-β-glucan was produced from a low (10 micromolar) UDP-glucose concentration, and relatively more 1,3-β-glucan was produced from a high (1 millimolar) UDP-glucose concentration. However, in ryegrass, 1,3;1,4-β-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-β-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 β-glucan increased with increasing pH. At the high UDP-glucose concentration, 1,3-β-glucan was the major product at pH 7 and below; 1,4-β-glucan synthesis was optimal at pH 8; and synthesis of 1,3;1,4-β-glucan was greatest above pH 8. With 10 micromolar GDP-glucose as substrate, 1,4-β-glucan, but no 1,3;1,4-β-glucan, was produced. Incorporation from either UDP-glucose or GDP-glucose was not influenced by the presence of the other.
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