Iron protoporphyrin IX albumin complexing increases the capacity and avidity of its binding to the periodontopathogen Porphyromonas gingivalis

Cells of Porphyromonas gingivalis strains W50 and WPH35 bound albumin and h aemalbumin complexes (with 2:1 and 1:1 molar ratios of protein to iron prot oporphyrin IX) in a concentration-dependent manner. The binding capacity fo r both haemalbumins was greater than for albumin. Scatchard analysis of bin ding to strain W50 revealed monophasic binding for albumin with an associat ion constant (K-a) similar to 10(5)/M. Binding of the haemalbumin complexes was biphasic. The K(a)s of the lower-affinity binding phases were similar to that for albumin, whilst those for the higher-affinity binding were appr oximately 20-30-fold greater. It is concluded that both the capacity and av idity for albumin binding to P. gingivalis are increased following haemalbu min complex formation. This phenomenon would enable cells to discriminate b etween albumin and haem-bearing albumin molecules as a potential source of haem. Such binding behaviour may confer a nutritional and ecological advant age in the periodontal pocket or gingival sulcus under conditions of haem l imitation. (C) 1999 Academic Press.