A fluorescent assay for complement activation

We report here a rapid assay for the complement enzymes CVFBb, C4b2a and Cls. This assay involves the use of a peptide substrate that releases a fluorescent coumarin derivative (AMC) upon cleavage by the convertase. The substrate, BocLeuGlyArgAMC, was chosen because its sequence is similar to the carboxyl terminus of C3a, and identical to that of C5a. The Km of this substrate are about 125 microM for the C3/5 convertase CVFBb, 169 microM for C4b2a, and 140 microM for C1s.