[Influence of pH and thermal treatment on the intramolecular mobility of pepsin]

In connection with a hypothesis of segmental flexibility of pepsin and its derivative aminopepsin (containing 3-aminotyrosine residues), a dynamic behaviour of pepsin and dansylated aminopepsin in aqueous solutions at pH 1.0--8.3 in investigated. It is shown that a dynamic structure of pepsin at pH 2.5--6.0 is almost invariant and very close to a structure studied in detail at pH 5.5. The lowering of a solution pH value from 2.5 to 1.0 is accompanied by labilization of pepsin and dansylated aminopepsin structures. Denaturation phenomena after thermal treatment of dansylated aminopepsin are also studied. An incubation of the latter in 0.1 M acetate buffer at pH 5.5 and temperature 50--80 degrees C with a subsequent cooling leads to irreversible conformational changes. The character of these changes is essentially dependent upon the incubation conditions.