Synthesis of α,β-unsaturated aldehydes as potential substrates for bacterial luciferases

Bacterial luciferase catalyzes the monooxygenation of long-chain aldehydes such as tetradecanal to the
corresponding acid accompanied by light emission with a maximum at 490 nm. In this study even numbered
aldehydes with eight, ten, twelve and fourteen carbon atoms were compared with analogs having a
double bond at the a,b-position. These a,b-unsaturated aldehydes were synthesized in three steps and
were examined as potential substrates in vitro. The luciferase of Photobacterium leiognathi was found
to convert these analogs and showed a reduced but significant bioluminescence activity compared to
tetradecanal. This study showed the trend that aldehydes, both saturated and unsaturated, with longer
chain lengths had higher activity in terms of bioluminescence than shorter chain lengths. The maximal
light intensity of (E)-tetradec-2-enal was approximately half with luciferase of P. leiognathi, compared
to tetradecanal. Luciferases of Vibrio harveyi and Aliivibrio fisheri accepted these newly synthesized substrates
but light emission dropped drastically compared to saturated aldehydes. The onset and the decay
rate of bioluminescence were much slower, when using unsaturated substrates, indicating a kinetic
effect. As a result the duration of the light emission is doubled. These results suggest that the substrate
scope of bacterial luciferases is broader than previously reported.