Porphyrins

[Leroy]

Can anyone tell me how porphyrins like chlorophyll and haeme are synthesized in nature. Is there a difference for plants and mammals since plants don't have haeme (i think).

[Ophiolite]

It's not simple:

http://w3.aces.uiuc.edu/NRES/LPPBP/Estrifd.html

[Leroy]

i had a look in my wonderful Biochemistry book (Stryer) and it has the biosynthetic route to heme.

 

Glycine reacts with succinyl CoA which yields delta-aminolevulinate. The reaction is catalysed by delta-aminolevulinate synthase which is present in mytochondria.

Two molecules delta-aminolevulinate condense to give the pyrrole porphobilinogen. The enzyme porphobilinogen deaminase catalyses the condensation of four porphobilinogens to form a linear tetrapyrrole.

This then cyclises to uroporphrinogen III. A few other steps are required to change the degree of saturation of the ring and also a few side groups are changed to eventually form protoporphyrin IX. Iron is added to it to give heme.

 

Actually more simple than I imagined. How plants do the same for chlorophyll is something I still have to look up if I have time.

[drjimbob]

There is a marked difference between the biosynthesis of haem and chlorophylls. The haem pathway in mammals starts at ALA synthase which catalyses the synthesis of ALA, as the name suggests, and requires succinyl-coA as a cofactor. The plant pathway goes via the C5 pathway to synthesise ALA. This involves three enzyme catalysed steps with glutamate-tRNA cofactor. Plants do synthesise haem, however it is utilised ina different way in comparison to the way in which it is used in mammals. The pathways diversify for haem and chlorophyll at metal ion insertion step - either iron (haem) or magnesium (chlorophyll).n Additionally the subcellular compartmentalisation is markedly different for the porphyrins. If you want any further information please contact me as I studied the pathways as part of my PhD. Hwoever that was a while ago.

 

Hope this helps