Mechanism and regulation of phosphate transport in Streptococcus pyogenes

In contrast to results reported with other bacteria, uptake of 32Pi in Streptococcus pyogenes was found to occur rapidly in starved cultures and to be strongly and immediately inhibited by addition of exogenous glycolytic energy sources (such as glucose) and nonglycolytic sources of ATP (such as arginine). Preincubation of starved cells with NaF, iodoacetate, or arsenate eliminated the inhibiting effect of glucose but not that of arginine. In accordance with the hypothesis that transport was attributable to Pi-Pi exchange, uptake and efflux of 32Pi in the presence of trans unlabeled Pi exhibited similar characteristics and were largely eliminated by reduction of the trans Pi concentration. Neither process was inhibited appreciably by pretreatment of cells with ionophores or metabolic inhibitors, but both processes were abolished by exposure to p-chloromercuribenzoate. Inhibition by both exogenous energy sources resulted in a reduction in the maximal velocity of transport (Vmax). Whereas arginine also caused a shift in the apparent Michaelis-Menten constant (Km) to larger values, glucose did not alter the Km. On the basis of the results reported, we propose that the rate of Pi exchange is determined positively by the intracellular and extracellular concentrations of Pi and negatively by ATP or metabolites thereof. The mechanism of ATP action is unknown but could involve either covalent or noncovalent modification of the carrier protein.