Purification of pro enzymic and activated human complement c 1s free of complement c 1r effects of calcium and ionic strength on activated complement c 1s Arlaud, G.J.; Reboul, A.; Meyer, C.M.; Colomb, M.G. Biochimica et Biophysica Acta 485(1): 215-226 1977 0005-2728 https://eurekamag.com/research/006/233/006233414.php