Individual alpha and beta subunits of bacterial luciferase exhibit bioluminescence activity

The alpha subunit of luciferase, encoded by the luxA gene, and the beta subunit, encoded by the luxB gene, have been expressed independently in Escherichia coli. We have found that the individual subunits of the heterodimeric (alpha beta) enzyme have bioluminescence activity. Overexpression of the individual subunits in Escherichia coli at 37 degrees resulted in accumulation of large amounts of the specific subunit in the insoluble fraction, while expression at lower temperatures (20 degrees-26 degrees) resulted in accumulation of high levels of the individual subunits in the soluble fraction of the cell lysates. We were surprised to find that addition of n-decanal to extracts of cells carrying either the luxA gene or the luxB gene followed by injection of FMNH2, conditions of the standard luciferase assay, resulted in emission of significant bioluminescence. The occurrence of the activity in lysates of E. coli cells carrying the gene for only one subunit showed that the activity of the isolated subunits is not due to contamination of one subunit with trace amounts of the other. The observed bioluminescence activity is the result of reactions catalyzed by the alpha subunit in the absence of beta subunit and also by the beta subunit in the absence of the alpha subunit.