Isolation, purification, and further characterization of an L-phenylalanine oxidase fromMorganella morganii

Abstract

A l-amino acid oxidase was isolated, purified, and characterized fromMorganella morganii 53187, a bacterium formerly known asProteus morganii. The synthesis of the enzyme by this bacterial strain was growth-associated and decreased sharply when the culture just reached the stationary phase. Based on this finding, the preparation of spheroplast by lysozyme-ethylene-diaminetetra-acetic acid (EDTA) disruption was carried out using the cells harvested during the exponential growth phase. Among several detergents tested, at the detergent-to-protein ratio of 2.5, 3-[(3-cholamidopropyl)dimethylammonio]-l-propane-sulfonate (CHAPS) was very effective in solubilizing most of the enzyme attached to the membranes while still preserving the activity of the solubilized enzyme. The resulting enzyme solution was then purified by hydrophobic interaction chromatography, followed by ion exchange chromatography and gel permeation.

The enzyme was purified 19-fold with an overall recovery yield of 12%, corresponding to a specific activity of 252.2 U/mg protein. The selectivity of the purified enzyme toward l-amino acids was pH-dependent. At pH 6.35, the enzyme was very specific to l-leucine, whereas the selectivity for l-phenylalanine could be improved at pH 7.4. The enzyme exhibited a wide optimum temperature range 35–43‡C and exhibited 1, l−dimethylferricinium reductase capability in the presence of l-phenylalanine.