Particulate membrane preparations isolated from cambial cells and differentiating and differentiated xylem cells of pine (Pinus sylvestris L.) trees synthesised [14C]glucans using either guanosine 5prime-diphosphate (GDP)-D-[U-14C]glucose or uridine 5prime-diphosphate (UDP)-D-[U-14C]glucose as glycosyl donors. Although these glucans had beta-(1rarr3) and beta-(1rarr4) linkages in an approximate ratio 1:1, the distribution of the linkages in the glucan synthesised from GDP-D-glucose was different from that synthesised from UDP-D-glucose. The synthesis of the mixed beta-(1rarr3) and beta-(1rarr4) glucan from GDP-D-[U-14C]glucose was changed to that of beta-(1rarr4) glucomannan in the presence of increasing concentrations of GDP-D-mannose. The glucan formed from UDP-D-[U-14C]glucose was not affected by any concentration of GDP-D-mannose. The membrane preparations epimerized GDP-D-glucose to GDP-D-mannose; however, the low amount of GDP-D-mannose formed was not incorporated into the polymer becaus the affinity of the synthase for GDP-D-glucose was much greater than that for GDP-D-mannose. The glucan formed from GDP-D-glucose and the glucomannan formed from GDP-D-glucose together with GDP-D-mannose were characterized. The apparent K m and V max of the glucan synthase for GDP-D-glucose were 6.38 mgrM and 5.08 mgrM·min-1, respectively. No lipid intermediates were detected during the synthesis of either glucan or glucomannan. The results indicated that an enzyme complex for the formation of the glucomannan was bound to the membrane.
A membrane-bound enzyme complex synthesizing glucan and glucomannan in pine tissue
DALESSANDRO, Giuseppe;PIRO, Gabriella;
1988-01-01
Abstract
Particulate membrane preparations isolated from cambial cells and differentiating and differentiated xylem cells of pine (Pinus sylvestris L.) trees synthesised [14C]glucans using either guanosine 5prime-diphosphate (GDP)-D-[U-14C]glucose or uridine 5prime-diphosphate (UDP)-D-[U-14C]glucose as glycosyl donors. Although these glucans had beta-(1rarr3) and beta-(1rarr4) linkages in an approximate ratio 1:1, the distribution of the linkages in the glucan synthesised from GDP-D-glucose was different from that synthesised from UDP-D-glucose. The synthesis of the mixed beta-(1rarr3) and beta-(1rarr4) glucan from GDP-D-[U-14C]glucose was changed to that of beta-(1rarr4) glucomannan in the presence of increasing concentrations of GDP-D-mannose. The glucan formed from UDP-D-[U-14C]glucose was not affected by any concentration of GDP-D-mannose. The membrane preparations epimerized GDP-D-glucose to GDP-D-mannose; however, the low amount of GDP-D-mannose formed was not incorporated into the polymer becaus the affinity of the synthase for GDP-D-glucose was much greater than that for GDP-D-mannose. The glucan formed from GDP-D-glucose and the glucomannan formed from GDP-D-glucose together with GDP-D-mannose were characterized. The apparent K m and V max of the glucan synthase for GDP-D-glucose were 6.38 mgrM and 5.08 mgrM·min-1, respectively. No lipid intermediates were detected during the synthesis of either glucan or glucomannan. The results indicated that an enzyme complex for the formation of the glucomannan was bound to the membrane.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
