Heme functions as a feedback inhibitor, repressing transcription of the ALA Synthase gene in most cells.
② 卟胆原(Porphobilinogen, PBG)的生成 ALA生成后从线粒体进入胞液
2H
+
Fe
N H3C N CH3
N H3C
CH2 CH2 COO
-
CH2 CH2 COO
-
Ferrochelatase
CH2 CH2 COO
-
CH2 CH2 COO
-
Fe2+ is added to protoporphyrin IX (原卟啉IX)via ferrocheletase (亚铁螯合酶), a homodimeric enzyme containing 2 iron-sulfur clusters, to yield heme.
H2C CH2 C O
C~SCoA O
ALA合酶 (磷酸吡哆醛)
反应部位:线粒体
CH2NH 2
H O P O O N H O C H2 C
O OH
CH3
Pyridoxal phosphate (PLP)
Pyridoxal phosphate (PLP,磷酸吡哆醛) serves as coenzyme for δAminolevulinate Synthase (ALA Synthase), an enzyme evolutionarily related to transaminases. CoA & the glycine carboxyl are lost following the condensation (缩合). ALA Synthase is the committed step of the heme synthesis pathway, and is usually rate-limiting for the overall pathway. ALA合酶是血红素合成 的关键酶。