Beta-glucan synthesis by cell-free extracts from Lolium multiflorum endosperm

1. 1. Particulate fractions from mid-log phase suspension cultures of Lolium multiflorum endosperm incorporate [ 14 C]glucose from UDP[U- 14 C]glucose into polymeric products and into unidentified compounds soluble in chloroform-methanol and 66% aqueous ethanol. 2. 2. The fraction from the cell homogenate sedimenting at 10 000–250 000 × g was most active in polysaccharide synthesis. 3. 3. Glucose was the only radioactive sugar detected in the high molecular weight product. 4. 4. The product was shown to be a mixture of β-glucans by fractionation on the basis of solubility in water and 1 M NaOH and from the pattern of products released by three β-glucan hydrolases with different substrate specificities for β-1, 3-, β-1, 4- and β-1, 3; 1,4-glucans. 5. 5. The proportion of 1,3- and 1,4-linkages in the total products was shown to vary with the concentration of UDPG. At 1 μM UDPG 90% of the residues in the total product were 1,4-linked, whereas the proportion fell to 49% at 1 mM UDPG. 6. 6. The water soluble polsaccharide which is the predominant product at 100 μM UDPG was examined by enzymic hydrolysis and shown to be a β-1,3;1,4-glucan similar to the glucan present in the Lolium endosperm cell walls. 7. 7. The UDPG concentration in the cells during growth has been measured. It reaches a maximum of 30 μM at mid-log phase.