FERRIC REDUCTASES OF LEGIONELLA-PNEUMOPHILA

Ferric reductase enzymes requiring a reductant for maximal activity we re purified from the cytoplasmic and periplasmic fractions of avirulen t and virulent Legionella pneumophila. The cytoplasmic and periplasmic enzymes are inhibited by zinc sulfate, constitutive and active under aerobic or anaerobic conditions. However, the periplasmic and cytoplas mic reductases are two distinct enzymes as shown by their molecular we ights, specific activities, reductant specificities and other characte ristics. The molecular weights of the cytoplasmic and periplasmic ferr ic reductases are approximately 38 and 25 kDa, respectively. The perip lasmic reductase (K(m) = 7.0 muM) has a greater specific activity and twice the affinity for ferric citrate as the cytoplasmic enzyme (K(m) = 15.3 muM). Glutathione serves as the optimum reductant for the perip lasmic reductase, but is inactive for the cytoplasmic enzyme. In contr ast, NADPH is the optimum reductant for the cytoplasmic enzyme. Ferric reductases ot avirulent cells show a 2-fold increase in their activit ies when NADPH is used as a reductant in comparison with NADH. In cont rast, ferric reductases from virulent cells demonstrated an equivalent activity with NADH or NADPH as reductants. With the exception of thei r response to NADPH, the ferric reductase at each respective location appears to be similar for avirulent and virulent cells.