Rate limiting step in heme synthesis is
catalyzed by ?
a) ALA dehydratase
b) ALA synthase
c) UPG decarboxylase
d) Ferrochelatase
Correct Answer - B
Ans. B. ALA synthase
Synthesis of heme
Heme synthesis takes place in all cells, but occurs to greatest extent
in bone marrow and liver.
The first step in the synthesis of heme is the condensation of glycine
and succinyl Co-A to form &-aminolevulinic acid (Delta-ALA), which
occurs in mitochondria.
This reaction is catalyzed by Delta-ALA synthase which requires
pyridoxal phosphate (PLP) as cofactor.
This is the rate limiting step in heme synthesis.