Summary: Froromectin (FN), a 420 kDa glycoprotein, consists of two similar subunits linked by a disulpthide bond near the C-terminal end. FN is present in soluble and matrix forms in various body fluids and tissues and has been shown to bind to a variety of organisms. We characterized the conditions required for I-FN binding to Bacille Calmette-Guerin (BCG). The binding was dose-dependent, reached saturation within 3 min, and was essentially irreversible for at least 24 h under optimal binding conditions at pH 60. In contrast, the binding was reversible (> 90% in 24 h) when the pH was increased to 10·0. Scatchard analysis of the dose-response expreiments produced a straight line, suggesting the presence of a single class of FN receptor on BCG. I-FN binding was trypsin-sensitive, suggesting that the BCG-binding molecule is a protein. The number of FN receptors was determined to be 8000-15000 per bacterium. I-FN binding was pH dependent, with maximal binding at acidic pH. I-FN binding was sensitive to the presence of NaCl, with 0·08 M-NaCl inhibiting binding by 85%. These data demonstrate that soluble FN binds to a trypsin-sensitive cell-surface component of BCG in an essentially irreversible manner.


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