A small creature I have in mind is highly toxic and constantly glows as a distinctly visible warning to everything else at night. It would use other warning methods but they're not really visible in the dark and is only active at night due to its nocturnal nature.
It is an insectivore scale-less reptile that has a similar body build to a gecko and has the ability to glide if it needs to.
The constant glowing skin is from the luciferase pumping through its veins and is produced by an organ specifically dedicated to do so. While I know organisms can produce luciferase, I don't know how metabolically expensive it is and if its constant production is feasible.
Is it feasible for an animal to constantly produce luciferase for bioluminescence purposes or would it be at risk of going into a metabolic or nutritional deficit because of it?