ATP-dependent protein kinase activities were detected in both membrane and cytoplasmic fractions from the oral pathogen Streptococcus mutuns. Different polypeptides were phosphorylated by endogenous kinase(s) in the two fractions. In membranes, five phosphoproteins were detected with apparent masses of 82, 37, and 10 kilodaltons (KD). In cytoplasm, two major acid-stable phosphoproteins were found. One was identified as HPr of the phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS), while the other had an apparent mass of 61 KD. Both of these proteins were phosphorylated on a seryl residue. Fructose 1,6-bisphosphate stimulated phosphorylation of HPr by the kinase and inhibited phosphorylation of the 61-KD protein. In contrast, fructose 1-phosphate, 2-phosphoglycerate, 3-phosphoglycerate, and dihydroxyacetone phosphate inhibited phosphorylation of HPr and stimulated phosphorylation of the 61-KD protein.
Several other glycolytic intermediates as well as inorganic phosphate inhibited phosphorylation of either or both proteins. Preincubation of cytoplasm with PEP prior to incubation with ATP reduced the amount of phospho-(sery1)-HPr formed, but not that of the 61-KD phosphoprotein. The latter protein has not yet been identified but has properties that suggest that it may be the protein kinase itself. These results provide evidence for one or more soluble ATP-dependent protein kinases in S mutuns that are regulated by glycolytic intermediates and that may play a role in the modulation of carbohydrate uptake and metabolism in this organism. A model for feedback regulation of sugar transport in S mutuns, mediated by an allosterically regulated kinase, is presented.