[Behavior of leucine aminopeptidase from bovine eye lens in guanidine hydrochloride. Dissociation and reassociation].

The dissociation and reassociation behavior of the hexameric leucine aminopeptidase (LAP) in solutions of 0.5 to 6 M guanidine-HC1 (Gu-HC1) was investigated by means of thin layer chromatography on Sephadex G-200 superfine. Up to 0.5 M Gu - hc1 the hexameric LAP-structure remains intact. In 0.75 to 2 M Gu - HC1 the enzyme dissociates nearly completely into its half-molecules (LAP-trimers, MW 160000 +/- 10,000). In 2.5 and 2.75 M Gu - HC1 a mixture of LAP-monomers (subunits) (MW 60000 +/- 5000) and trimers was to be found. Treatment with beta-mercapto ethanol increases the portion of monomers. Only monomers occurred in 3 to 6 M Gu - HC1. Parallel to the dissociation, a loss of the essential zinc (half life: 10.5 and 3.5 hours in 1 M and 4 M Gu - HC1 resp.) and a decrease of the enzymatic activity (30 min after treatment with 1 M and 4 M Gu - HC1 50% and 1% resp. residual activity) of the observed. On the other hand, the enzyme was activated by dilute solutions of Gu - HC1 (0.1 to 0.3 M: max. increase 50%). Removal of the denaturant causes reassociation of all types of fragments to hexameric LAP which was indistinguishable from the native LAP in Ouchterlony immune diffusion test. The reassociation was accompanied by a small increase in activity only.