l-Asparaginase from Escherichia coli B

Abstract

Abstract l-Asparaginase from Escherichia coli B has a fluorescence maximum at 320 nm in addition to shoulders at 307 and 325 nm. Reversible dissociation of the tetrameric aggregate in 3.2 m urea is accompanied by the loss of the 320 nm emission band and the appearance of a band at 305 nm due to tyrosine and one at 345 nm characteristic of tryptophan in aqueous solution. Shifts in the ultraviolet absorption spectrum also accompany dissociation into subunits. The rate of dissociation was monitored by the absorption and emission properties. The rate was found to be independent of enzyme concentration and is roughly dependent on the twelfth power of the urea concentration. Enhancement of the rate of dissociation by alcohols was related to the length of the alkyl chain. The tetramer is rapidly and irreversibly dissociated by 0.1% sodium dodecyl sulfate into monomeric subunits. Changes in the emission and absorption spectra indicate that detergent binds in the vicinity of tyrosyl and tryptophyl residues.