, an important aetiological agent of dental caries, is known to transport glucose via the phosphoenolpyruvate (PEP) phosphotransferase system (PTS). An alternative non-PTS glucose transport system in Ingbritt was suggested by the increased ATP-dependent phosphorylation of glucose and the presence of higher cellular concentration of free glucose in cells grown in continuous culture under PTS-repressed conditions compared to those resulting in optimal PTS activity. A method was developed for the preparation of membrane vesicles in order to study this system in the absence of PTS activity. These vesicles had very low activity of the cytoplasmic enzymes, glucokinase, pyruvate kinase and lactate dehydrogenase. This, coupled with the lack of glycolytic activity and the inability to transport glucose, suggested that the vesicles would also be deficient in PTS activity because of the absence of the general soluble PTS proteins, Enzyme I and HPr, required for the transport of all PTS sugars. Freeze fracture electron microscopy and membrane H-ATPase analysis indicated that over 90% of the vesicles had a right-side-out orientation. Vesicles from cells grown in continuous culture under PTS-dominant and PTS-repressed condition both exhibited glucose counterflow. This indicates the presence of a constitutive non-PTS carrier in the organism capable of transporting glucose and utilizing ATP for glucose phosphorylation. Analysis of growth yields of cells grown under PTS-repressed and PTS-optimal conditions suggests that ATP or an equivalent high energy molecule, must be involved in the actual transport process. This analysis is consistent with an ATP-binding protein model such as the transport system reported by R. R. B. Russell and coworkers ( 267, 4631-4637), but it does not exclude the possibilit of a separate permease for glucose.


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