Enzymic Dissociation of Zea Shoot Cell Wall Polysaccharides : III. Purification and Partial Characterization of an Endo-(1 --> 4)-beta-d-Xylanase from a Bacillus subtilis Enzyme Preparation

¹⁴C-photoassimilate release from isolated tobacco (Nicotiana tabacum L. cv Xanthi nc.) mesophyll cells was gradual and much of the photoassimilate was retained for several hours. ¹⁴C-product retention was enhanced by Ca²⁺ and impaired by EDTA and ATP. Mg²⁺ reduced the ATP-enhanced ¹⁴C-efflux suggesting that ATP impairs product retention by modifying cell membrane permeability, possibly as a result of its chelating properties.

Various metabolic inhibitors increased ¹⁴C-efflux indicating an energy requirement for ¹⁴C-product retention. Profiles of ¹⁴C-product distribution in the cells and suspending medium indicated that ¹⁴C-efflux from cells treated with carbonylcyanide p-trifluoromethoxyphenylhydrazone occurred by passive diffusion. Coupled with the observation that exogenous sucrose increased ¹⁴C-efflux and the demonstration of ¹⁴C-sucrose uptake, the results suggest that product retention is partially due to the activity of an energy-dependent uptake process which recovers much of the photoassimilate lost from the cells.

Under certain conditions, carbonylcyanide p-trifluoromethoxyphenylhydrazone reduced ¹⁴C-efflux. The apparently contradictory effects of the uncoupler appeared to be related to the intracellular photoassimilate concentration and may be explained by the partitioning of photoassimilate within the cells.