HEMIN REGULATION OF HEMOGLOBIN BINDING BY PORPHYROMONAS-GINGIVALIS

Hemoglobin binding to chemostat-grown hemin-excess and hemin-limited c ells of Porphyromonas gingivalis W50, and to cells of the avirulent, b eige-pigmenting variant W50/BE1, was quantified. Hemin-excess W50 boun d more hemoglobin than hemin-limited W50, mirroring the hemin-binding ability of these cells [Microb Ecol Health Dis 7:9-15, 1994]. In contr ast to hemin, hemoglobin binding was not enhanced by sodium dithionite . The hemoglobin-binding capacity of hemin-excess W50/BE1 was below th at of hemin-limited W50 and only observed under oxidizing conditions. Scatchard analysis revealed similar affinity constants for hemin-exces s and hemin-limited W50, and confirmed a lower binding maximum for the latter. Hemin-excess WSO/BE1 displayed cooperative binding of hemoglo bin. These differences in binding were reflected in the binding of a h orse radish peroxidase-conjugated hemoglobin (HHRPO) in a dot-blot ass ay. However, neither the 32-kDa hemin-binding protein, nor its 19-kDa heat-modified form, from either hemin-limited W50 or hemin-excess W50/ BE1, bound this conjugate. These data indicate that hemoglobin binding by P. gingivalis is hemin-regulated and occurs via a mechanism differ ent from hemin binding.