Can luciferin be used as a substrate?

Yes, luciferin can be used as a substrate. The chemical reaction that results in bioluminescence requires two unique chemicals: luciferin and either luciferase or photoprotein. Luciferase enzyme binds to luciferin. The luciferase enzyme then speeds up a chemical reaction in the combining of luciferin and the oxygen molecule. The resultant product is known as the oxyluciferin. The process of combining oxygen and luciferin is what produces light. The bioluminescent color (yellow in fireflies, greenish in lanternfish) is a result of the arrangement of luciferin molecules.