Aminolevulinic acid (also dALA, δ-ALA, 5ALA or 5-aminolevulinic acid), an endogenous non-protein amino acid, is the first compound in the porphyrin synthesis pathway, the pathway that leads to heme in mammals and chlorophyll in plants. In plants, production of 5ALA is the step on which the speed of synthesis of chlorophyll is regulated. Plants that are fed by external 5ALA accumulate toxic amounts of chlorophyll precursor, protochlorophyllide, indicating that the synthesis of this intermediate is not suppressed anywhere downwards in the chain of reaction. Protochlorophyllide is a strong photosensitizer in plants.