[The fluorescence of pepsin conjugates with DNS-chloride]

Parameters of rotational relaxation of pepsin conjugated in neutral and slightly alkaline solutions with a fluorescent label 1-dimethylaminonaphthalene-5-sulphonyl chloride (DNS-Cl) are measured by a fluorescence polarization method. It is shown that the globule of pepsin denatured and loose at lakaline pH values converts into a compact form after transfer to acidic solution. The compactness of this new form is close to that of native inhibited pepsin. A new globule is distinguished from the native by the absence of segmental flexibility. Conjugated with a DNS at pH less than or equal to 7.0 pepsin relaxes in solution as catalytically active dansylated aminopepsin (DNS-3-aminotyrosine pepsin). Evidence is presented that these conjugates are also characterized by segmental flexibility.