Initial Characterization of Hexose and Hexitol Phosphoenolpyruvate-Dependent Phosphotransferases of Staphylococcus aureus

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The phosphoenolpyruvate sugar phosphotransferases of Staphylococcus aureus were surveyed biochemically to determine substrate range, inducibility and constitutivity, and requirements for soluble sugar-specific proteins. The substrate range is similar to that of the phosphotransferases of enteric bacteria, but the staphylococcal mannose and sorbitol systems are very inefficient. In addition, S. qureus has phosphotransferase activities for lactose and sucrose. The systems tested fell into two broad classes. Sugars for which there was substantial constitutive activity (fructose, mannose, sucrose, and glucose and its nonmetabolized analogues) did not require sugar-specific soluble factors for phosphorylation. Only in the case of fructose did growth in the presence of these constitutive sugars induce the corresponding phosphotransferase activity to higher levels. Kinetic experiments with each of these constitutive sugars yielded biphasic Hofstee plots; i.e., the kinetics were not characteristic of single enzymes. Preliminary experiments suggest that sucrose phosphorylation may involve the glucose and/or fructose systems. Truly inducible sugar phosphotransferase systems represent a second class; those for lactose and mannitol are the only members thus far identified. These systems are absent from uninduced cells, require soluble sugar-specific factors, and exhibit linear Hofstee plots. Sorbitol is apparently transported very poorly by intact cells but is an inducer of the mannitol system; it is phosphorylated efficiently in vitro by extracts of cells grown on either hexitol, but is taken up by intact cells at 0.1% of the mannitol rate.

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