BINDING OF HEMOGLOBIN BY PORPHYROMONAS-GINGIVALIS

In this study, we investigated whether Porphyromonas gingivalis can bi nd hemoglobin as an initial step in the acquisition of heme from hemog lobin. The binding of human hemoglobin by P. gingivalis cells was dete rmined using [H-3]hemoglobin. Hemoglobin binding occurred rapidly, rev ersibly and specifically. A Scatchard analysis of the binding data gen erated a linear plot, indicating a single population of binding protei ns. The apparent K-d was 1.0+/-0.19X10(-6) M and there were 3.2+/-0.76 X10(4) binding sites per cell. Hemoglobin binding was inhibited by unl abeled human hemoglobin but not by hemin and protoporphyrin IX. The bi nding was only partially inhibited by human serum albumin, transferrin , lactoferrin, catalase and cytochrome c. These results suggest that t he ligand recognized by the binding protein may not be the heme moiety . The binding of hemoglobin considerably increased when the organisms were grown under hemin-limited conditions. Hemoglobin bound to outer m embrane proteins extracted from P. gingivalis cells on a dot blot bind ing assay and binding ability was lost after heating bacterial protein s. These results suggest that P. gingivalis cells interact with human hemoglobin through specific binding sites on their surfaces as a preli minary step in iron acquisition.