Action of Serum upon Proteolysis

1. The hydrolysis of casein at pH 4.5-5.0 by gastric mucosa of a rabbit is activated apparently in the presence of serum or plasma, while that of pepton and also that of casein or serum albumin at pH near 2.0 always remain unaffected. 2. The hydrolysis of casein at pH 4.5 by rabbit liver is inhibited by serum but that of pepton at pH 4.5 or 7.8 is not. These two pepton splitting activities can be separated from each other by alkaline or acid treatment. 3. The hydrolysis of casein and serum albumin at pH 4.4-5.0 by gastric mucosa (human) are to some extent inhibited by serum or scarecely undergo influence, while that of egg albumin is activated by serum. The hydrolysis of pepton at pH 4.6 and that of casein or serum albumin at pH 2.0, all remain without being influenced. 4. Catheptic pepton splitting enzyme action (cathopeptonase) may presumably be in a rabbit's liver, in its gastric mucosa and also in human gastric mucosa.