Photochemical inactivation of Aeromonas aminopeptidase

Abstract

Aeromonas aminopeptidase (AAP) which has been discovered and studied by Prescott and his coworkers [1,2], was recently shown to undergo irreversible photochemical inactivation in the presence of 2,3butanedione (BD) [3]. This reaction is of interest since BD and related diketones and ketone aldehydes have been widely used as specific probes for the active arginyl residues of enzymes. The previous [3] and the present studies on the BD-sensitized photochemical inactivation of AAP revealed, however, that this pro. cess is accompanied by extensive structural changes in the enzyme protein, including destruction of possibly all enzyme tryptophyl residues. The purpose of this communication was to provide additional information about the BD-sensitized photochemical inactivation of AAP. It was shown that the destruction of peptidase and esterase activities occurred simultaneously. The results were also consistent with an all-or-none loss of activity hypothesis (i.e.no partially inactivated enzyme active sites exist). Progressive enzyme inacti. vation was accompanied by a progressive destruction of the enzyme. It is predictable that these phenomena are common among proteins and peptides containing tryptophan which may be a primary target of the triplet stage sensitizers (3BD in the present case). These results also warn us from drawing conclusions from enzyme modification data obtained with BD and related compounds, unless the photochemical and photophysical aspects are carefully considered.