Factor D cleaves C3(H2O)-bound Factor B

Factor D, a constitutively active serine protease found in trace amounts in the blood, cleaves a specific Arg-Lys bond in the Factor B component of the soluble C3(H2O):Factor B complex, yielding C3(H2O):Factor Bb and an inactive polypeptide, Factor Ba (Fearon and Austin 1975; Lesavre and Muller-Eberhard 1978; Lesavre et al. 1979; Schreiber et al. 1978).因子D，一种在血液中以微量存在的持续活性丝氨酸蛋白酶，能够特异性地切割可溶性C3(H2O):因子B复合物中因子B成分的特定精氨酸-赖氨酸键，从而生成C3(H2O):因子Bb和一种无活性多肽，即因子Ba（Fearon和Austin 1975；Lesavre和Müller-Eberhard 1978；Lesavre等1979；Schreiber等1978）。