Determination of plasma and serum l-lysine using l-lysine ε-oxidase from Marinomonas mediterranea NBRC 103028T

This article describes a successful application of l-lysine ε-oxidase (EC 1.4.3.20) for l-lysine determination. l-Lysine ε-oxidase was isolated from culture supernatant of Marinomonas mediterranea NBRC 103028T and was used for l-lysine determination. Comparison of the characteristics of l-lysine ε-oxidase with l-lysine α-oxidase, a commercial enzyme used for l-lysine determination, suggests that the use of l-lysine ε-oxidase would be more valuable for the determination of l-lysine because of its selectivity and sensitivity, especially in samples with low l-lysine concentration. The enzyme acted only on l-lysine and l-ornithine, to which the relative activity was only 3.4% of that on l-lysine. The value obtained by the colorimetric assay using l-lysine ε-oxidase and horseradish peroxidase was not affected by l-ornithine. The enzyme also shows a higher affinity for l-lysine (Km = 0.0018 mM). l-Lysine determination using l-lysine ε-oxidase in human plasma and serum was examined. The measured values were close to values determined by instrumental analyses using the precolumn AccQ·Tag Ultra Derivatization Kit. These results suggest that l-lysine ε-oxidase can be used for diagnosis based on plasma l-lysine concentration. This is the first report on the application of l-lysine ε-oxidase.