2Abz-SLGRKIQIK(Dnp)-NH2 is a bioactive peptide. [This peptide serves as a physiological substrate for the second complement component (C2), which is the zymogen of the first complement component, Cls. The complement system is a central element of host defense but can also result in inflammation under pathological conditions. The C1s protease of the C1 complex initiates the host defense pathway. This peptide utilizes a 2Abz/Dnp FRET pair to quantify complement enzyme activity.]