T. Takeda et al., XYLOGLUCAN ENDOTRANSGLYCOSYLATION IN SUSPENSION-CULTURED POPLAR CELLS, Bioscience, biotechnology, and biochemistry, 60(12), 1996, pp. 1950-1955
Xyloglucan endotransglycosylase activity was identified and defined by
transfer of a part of xyloglucan to reduced xyloglucan heptasaccharid
e ([H-3]XXXGol) in an enzyme preparations from suspension-cultured pop
lar cells, Although the activity was distributed in buffer-soluble and
buffer-insoluble fractions associated with cells and in the extracell
ular fraction, it was mostly recovered in the buffer-insoluble fractio
n, suggesting that the enzyme was bound to the cell wall, The affinity
for acceptor XXXGol was increased at a higher concentration of donor
xyloglucan with a constant V-max. The V-max for donor xyloglucan was i
ncreased at a higher concentration of the oligosaccharide without any
change in affinity. These kinetic data suggest that the acceptor acts
by combining with the enzyme independently of the donor, The velocity
of the reaction decreased gradually as the heptasaccharide units was i
ncreased from two to four, suggesting that the xyloglucan endotransgly
cosylase reaction caused donor xyloglucan substantially to decrease in
molecular size, The activity in buffer-soluble fraction was increased
by ABA in auxin-starved cells, when cultured in MS medium containing
various plant hormones, Nevertheless, the activity increased markedly
at the exponential growth and decreased immediately at the stationary
phase of cells in the presence of 2,4-D, The activity of xyloglucan en
dotransglycosylase is developmentally regulated during growth but is n
ot directly induced by plant hormones.