Pathology > Basic Hematology > Normal Hematopoiesis > Erythrocyte Review > Porphyrin Synthesis & Structure

Porphyrin Synthesis & Structure

Heme, the prosthetic portion of hemoglobin, is synthesized in nucleated red cells in the bone marow.

Four pyrrole units are arranged to form ringed structures: heme, porphyrinogen, and porphyrin. When broken down (catabolism) these ringed structures form linear tetrapyrrole molecules, the bile pigments, ie. biliverdin.

The biosynthesis of heme is outlined schematically on the following cards: 1) synthetic sequence, 2) synthetic location, and 3) enzymes.

Notes: a) The rate limiting synthetic step is the formation from glycine and succinyl coA of d- aminolevulinic acid (ALA).
b) Several key steps take place in mitochondria or on mitochondrial membranes.
c) Porphyrinogens are colorless, unstable, ringed tetrapyrroles that are readily and irreversibly oxidized to red, stable porphyrins, which are excreted in urine or bile.
d) Only one porphyrin, protoporphyrin IX, is retained and is converted to heme.


Synthetic Sequence

Synthetic Location

Key Enzymes

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