Error associated with experimental flux control coefficient determinations in the Calvin cycle.

Model studies of photosynthetic carbohydrate formation in the chloroplast of C3 plants have been performed to examine the expected response of the steady-state reaction flux to finite changes in concentration or activity of individual enzymes in a central metabolic network. The results indicate that flux control coefficients in this system cannot be reliably estimated experimentally even for the two enzymes that do exert predominant control under the examined conditions. Reduction of the mathematical error of the estimates to a satisfactorily low level requires such small enzyme concentration changes that presently available assay methods do not allow for a determination of the corresponding flux changes with satisfactory precision. It is concluded from these observations and general methodological considerations that experimental flux control coefficient estimates cannot be trusted unless evidence is presented to show that the mathematical error associated with their determination is of insignificant magnitude.