Steady State Kinetics of Mannitol Phosphorylation Catalyzed by Enzyme IImt ’ of the Escherichia coli Phosphoenolpyruvate-dependent

The kinetics of mannitol phosphorylation catalyzed by enzyme IIm ” of the bacterial P-enolpyruvate-de-pendent phosphotransferase system are described for three different physical conditions of the enzyme, (i) embedded in the membrane of inside-out (ISO) oriented vesicles, (ii) solubilized and assayed above the critical micellular concentration (cmc) of the detergent, and (iii) solubilized and assayed below the cmc of the deter-gent. The kinetic characteristics of enzyme IImtl, after solubilization of cytoplasmic membranes or after pu-rification from these membranes are comparable. The mannitol-dependent kinetics at saturating concentra-tion of P-HPr were biphasic both for the solubilized enzyme assayed above the cmc and for the enzyme in IS0 vesicles. In contrast, the mannitol-dependent ki