user: Question: What is Protoporphyrin IX's substrate?
Columns: ['Enzyme', 'Location', 'Substrate', 'Product', 'Chromosome', 'OMIM', 'Porphyria']
Types: ['text', 'text', 'text', 'text', 'text', 'real', 'text']
Sample row: ['ALA synthase', 'Mitochondrion', 'Glycine , succinyl CoA', 'δ-Aminolevulinic acid', '3p21.1', 125290.0, 'none']
SQL:

assistant: SELECT "Substrate" FROM "Table" WHERE "Product" = 'Protoporphyrin IX';