Subtilisin, III

While many examples of limited proteolysis are known, e.g., tiypsin on the B-chain of insulin (Sanger and Tuppy, 1951), zymogen activation (Neurath, 1957), ovalbumin-plakalbumin conversion (Ottesen, 1958), etc., a reversible equilibrium, as in step 1, has not yet been demonstrated except possibly in the pepsinogen-pepsin conversion (Herriott, 1938,1941). It probably does not exist because the peptide is too short the argument for a critical size of the peptide, in order to observe reversibility, has been presented in Chapter III. However, recent experiments of Richards (1958) on the subtilisin digestion of ribonuclease, wherein the 20 residue N-terminal tail is removed by hydrolysis, indicate that side-chain hydrogen bonding may possibly be involved in the association between the tail and the core. 

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