CHEMICAL MODIFICATION OF HUMAN-COMPLEMENT FACTOR-H - EFFECT ON COMPLEMENT REGULATORY ACTIVITY

Human complement factor H is a major regulatory protein of the alterna tive pathway of complement. It consists of 20 protein modules known as complement control protein modules (CPs). Previous studies have indic ated that the complement regulatory activity is contained within the f irst five CPs of factor H and additionally that chemical modification of lysine residues with the modifying reagent O-methylisourea inhibits the complement regulatory activity of factor H. In this study chemica l modifications of lysines, arginines, carboxyl groups and histidine r esidues of factor H were performed and the effect on the complement re gulatory activity of factor H was assessed by studying the rate of bre akdown of I-125-labelled C3 (NH3) in the presence of factors H and I. Residue types important for the complement regulatory activity of fact or H were identified.