Cytochrome c used as a model system to probe the structural properties of benthic mucilage

Benthic mucilage, whether native or artificially fragmented to microscopic dimensions by ultrasonic treatment, was mixed with cytochrome c, which was used as a 12 000 Da polycationic model compound. Cytochrome c binding profiles proved to depend on the aggregation state of the mucilage. The native mucus matrix binds cytochrome c quasi hyperbolically with an apparent affinity constant K = 1 × 10⁶  M ⁻¹. As shown by chemical modification of both the mucilage and cytochrome c, the binding expression is dependent on the availability of both the positive charges on the cytochrome c surface and the negative charges within the mucus matrix. The extent of binding is sensitive to the ionic strength of the medium. The ultrasonic-stabilized mucus fragments display a peculiar binding profile, with an apparent low affinity, abruptly entering into a high affinity binding region. The results suggest that, depending on the mucus to polycation ratio, a polymeric reticulus builds up. This reticulus can accommodate molecules of at least 12 000 Da molecular weight. The results are also discussed with respect to biological implications. Received: 23 April 1997 / Accepted: 24 November 1997