Membrane-bound O-methyltransferase of douglas-fir callus

A lignin-specific O-methyltransferase (OMT) was localized in the cell wall fraction of Douglas-fir needle callus homogenates. The OMT was released from wall-associated membrane by digitonin and partially purified by salt fractionation. Further purification proved to be unfeasible, due to the high tannin content of the callus. The K_m values of the partially purified OMT for caffeic acid and S-adenosylmethionine (SAM) were 250 and 8.0.μM, respectively. Substrate inhibition as well as inhibition by S-adenosylhomocysteine (SAH) was observed. Coupled with low levels of caffeic acid found in the callus, 65,μM at maximum with a mean of 11.5μM throughout a subculture period, the properties of this OMT should account in large part for the high tannin and low lignin content characteristic of this cultured tissue.