MECHANISMS OF IRON-A CQUISITION FROM HEMOGLOBIN IN PORPHYROMONAS GINGIVALIS

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In this study, we investigated on the mechanisms of the acquisition of heme from hemoglobin in Porphyromonas gingivalis. The iron-depleted cells of P.gingivalis 381 were incubated in the basal medium plus test substrates such as hemoglobin, hemin, transferrin and various inorganic iron-compounds. The value of Ks, a parameter analogous to Michaelis-Menten constant, was estimated.P.gingivalis 381 showed a Ks value of 3.85,4.91 and 0.0017 mM for hemin, transferrin and hemoglobin, respectively. However, the inorganic iron compounds tested did not support P.gingvalis growth. These findings suggest that P.gingivalis utilizes hemoglobin as an iron source much more effectively than other iron-containing compounds under an iron -limited environment. Next, binding of human hemoglobin by P.gingivalis cells was determined by using [^3H]-labeled hemoglobin. The binding of hemoglobin occurred rapidly, reversibly and specifically. Scatchard analysis of the binding data revealed linear plot, indicating the presence of one population of binding protein. The apparent Kd was 1.0? B10.19x10^<-6>M and number of binding sites per cell was 3.2? B10.76x10^4. Hemoglobin binding was inhibited by unlabeled human hemoglobin but not hemin and protoporphyrin IX.The binding was only partially inhibited by serum albumin, transferrin, lactoferrin, catalase and cytochrome c. These results suggest that the ligand recognized by the binding protein may not be the heme moiety. The binding of hemoglobin much increased when the organisms were grown in hemin-limited conditions. These results suggest that P.gingivalis cells may interact with human hemoglobin through specific binding sites on their surfaces as a preliminary step in iron acquisition.