Rate limiting step in porphyrin synthesis is

The synthesis stas with the condensation of succinyl CoA and glycine in the presence of pyridoxal phosphate to form delta amino levulinic acid (ALA).The enzyme ALA synthase is located in the mitochondria and is the rate limiting ezyme of pathway. Next few steps occurs in cytoplasm.2 molecules of ALA are condensed to form porphobilinogen (PBG) Condensation of 4 molecules of PBG results in the formation of the first porphyrin of the pathway,namely urobilinogen. REFERENCE:DM VASUDEVAN Textbook SEVENTH EDITION, Page no:272 and 273