Sulfobacins A and B, novel von Willebrand factor (vWF) receptor antagonists, have been isolated from the culture broth of Chryseobacterium sp. (Flavobacterium sp.)† NR 2993 by ethyl acetate extraction, and by Sephadex LH-20 and silica gel column chromatographies. The physico-chemical properties of the sulfobacins indicate that their structures are completely different from that of aurintricarboxylic acid, the one known vWF receptor antagonist. Sulfobacins A and B inhibit the binding of vWF to its receptor with IC50s of 0.47 and 2.2 μM, respectively. Sulfobacin A also inhibits ristocetin-induced agglutination in human platelets fixed with paraformaldehyde with an IC50 of 0.58 μM.
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