VARIOUS VECTORIAL BEHAVIORS OF A SPATIALLY STRUCTURED SUBSTRATE CYCLE

The dynamic properties of the glucose/glucose-6-phosphate cycle are st udied under conditions where the phosphatase and kinase interconvertin g enzymes an spatially distributed. A semi-artificial membrane made of compacted plant cell walls bearing active phosphatase in its natural state, separates two compartments, one of these compartments containin g soluble hexokinase. Depending only upon the two enzyme activity leve ls and the initial distribution of the substrates, numerous asymmetric al and vectorial behaviours can be observed, such as facilitated gluco se 6-phosphate diffusion, active transport of either glucose or glucos e B-phosphate and sequential (alternative) transport between glucose a nd glucose 6-phosphate, A diffusion-partition reaction coupling can ac count for these oriented mass transfers. The possibility of such a cou pling in this model system is clearly dictated by the global analog of the Curie principle. These results may provide new insight on (a) the still obscure role played by the cell-wall phosphatase activities, pa rticularly their involvement in the transport of exogenous phosphomono esters, and (b) the actual in vivo operation of substrate and protein cycles in view of the heterogeneity and anisotropy of the cellular mil ieu.