Use of an IgG fragment prepared with particulate plasmin to study the C1 binding and activation.

Facb, fragment antigen and complement binding (this last property is shown when the fragment is involved in an immune complex); Fc, C-terminal half of the heavy-chain dimer; pFc′, major C-terminal fragment released from IgG by pepsin or plasmin digestion; DFP, diisopropylphosphofluoridate; ATEE, N-acetyl-L-tyrosine ethyl ester; BAEE, N-benzoyl-L-arginine ethyl ester; TAME, p-toluene sulfonyl-L-arginine methyl ester; SDS, sodium dodecyl sulfate; SBTI, soybean trypsin inhibitor.The nomenclature of the complement components (C1, C1q, C1r, C1s) follows the W.H.O. recommendations. Enzymatic activities are expressed in nanokatals (nkat.) as recommended in the Enzyme Nomenclature (1973).