The eighth component of human complement. Purification and physicochemical characterization of its unusual subunit structure.

摘要: The eighth component of human complement (C8) has been purified in high yield from Cohn Fraction III and characterized with regard to its physicochemical properties subunit structure. product was found be similar functional C8 isolated plasma or serum. Human possesses a molecular weight 151,000 is composed 1:1:1 ratio three nonidentical subunits: alpha (Mr = 64,000), beta gamma 22,000). These subunits occur as covalently linked alpha-gamma dimer which noncovalently associated beta. After purification characterization alpha, beta, gamma, each possess different amino acid compositions NH2-terminal sequences. Both contain but exceptionally percentages hydrophobic aromatic acids. As measured by circular dichroism, the secondary structure contains 12% alpha-helix, 24% structure, 64% unordered values typical globular proteins. Complete well hemolytic activity, can recovered after exposure 6 M guanidinium hydrochloride 8 urea. were dissociated presence sodium dodecyl sulfate removal detergent, neither independent activity. Significantly, activity equivalent that native generated when recombined an equimolar ratio. results indicate atypical serum protein both denaturation characteristics.