Transport of glutamine by Streptococcus bovis and conversion of glutamine to pyroglutamic acid and ammonia

Streptococcus bovis JB1 cells energized with glucose transported glutamine at a rate of 7 nmol/mg of protein per min at a pH of 5.0 to 7.5; sodium had little effect on the transport rate. Because valinomycin-treated cells loaded with K and diluted into Na (pH 6.5) to create an artificial delta psi took up little glutamine, it appeared that transport was driven by phosphate-bond energy rather than proton motive force. The kinetics of glutamine transport by glucose-energized cells were biphasic, and it appeared that facilitated diffusion was also involved, particularly at high glutamine concentrations. Glucose-depleted cultures took up glutamine and produced ammonia, but the rate of transport per unit of glutamine (V/S) by nonenergized cells was at least 1,000-fold less than the V/S by glucose-energized cells. Glutamine was converted to pyroglutamate and ammonia by a pathway that did not involve a glutaminase reaction or glutamate production. No ammonia production from pyroglutamate was detected. S. bovis was unable to take up glutamate, but intracellular glutamate concentrations were as high as 7 mM. Glutamate was produced from ammonia via a glutamate dehydrogenase reaction. Cells contained high concentrations of 2-oxoglutarate and NADPH that inhibited glutamate deamination and favored glutamate formation. Since the carbon skeleton of glutamine was lost as pyroglutamate, glutamate formation occurred at the expense of glucose. Arginine deamination is often used as a taxonomic tool in classifying streptococci, and it had generally been assumed that other amino acids could not be fermented. To our knowledge, this is the first report of glutamine conversion to pyroglutamate and ammonia in streptococci.