Degradation of Protein SAA to an AA‐like Fragment by Enzymes of Monocytic Origin

Abstract

On incubation in cultures of blood mononuclear leukocytes from normal [human] individuals, protein SAA [amyloid protein A related serum component] is gradually degraded and yields an intermediate fragment with the same MW as that of protein AA [amyloid protein A]. This protein fragment has the same antigenic properties as protein AA, as judged from double-immunodiffusion analysis. Cell fractionation studies attribute the degrading capacity to the monocytes. The proteolytically active substance was released to the medium by cells in culture. The proteolytic substance, which also degraded protein AA, could be inhibited by diisopropylfluorophosphate and phenylmethyl-sulfonylfluoride. This suggested that the enzyme might be a serine protease.