Control and regulation of metabolic fluxes in microbes by substrates and enzymes

The control of enzymes and substrates on the flux through microbial metabolic pathways can be quantified in terms of flux control coefficients. In pathways involving group transfer, the summation theorem for flux control by the enzymes has to be modified: the sum of control by all enzymes is between 1 and 2. The phosphoenolpyruvate:glucose phosphotransferase system is such a pathway. Experimental determination of the control by the enzymes in this pathway is under way. The control of the enzymes on the glycolytic flux in yeast is low, with the possible exception of the uptake step. In Klebsiella pneumoniae potassium and ammonium ions can simultaneously be 'limiting', (i.e. have significant control on growth) at pH 6, but not at pH 8. This may be due to the fact that at pH 8 the high-affinity potassium uptake system is absent.