What does the blood have to do with porphyrins?

Question

The blood in your body has porphyrins in it, I think it helps makes the blood, but what exactly does the porphryins do, where do they come from, what are they made of, if you have to many i.e. porphyria, what will cure it. I know I know there's no cure, but there is, there's got to be we just haven't found it yet. But mainly what is the purpose of porphyrins and what are they made of?

Answer 1

Porphyrins are intermediates in making blood.

The functional part of red blood cells- the one that carries oxygen is a molecule called hemoglobin. Hemoglobin contains a functional unit called 'heme' which is iron bound in a somewhat circular molecule. The heme is made separately from the hemoglobin.

Heme is made in the liver along an approximately ten-step process. The molecules in that process that aren't finished are called 'porphyrins'. So basically, a porphyrin is a molecule that goes in a red blood cell that's not essentially 'done' yet. Another definition is that the porphyrin is the circular molecule that the iron 'fits' into.

On that ten step pathway, one of the enzymes in the ten steps can be defective - they generally work very, very slowly. This results in a build up of the porphyrin that the enzyme works at. Sort of like there being an incompetent person at airport security. All the people who have to go through build up waiting for that one slow step. The porphyrins build up in the cytoplasm of liver cells. These molecules can be toxic in a certain sense - they muck with other jobs the cell is doing, and this is what we call the disease 'porphyria'. Note that there are many porphyrias, with many different symptoms depending on which enzyme is broken.

The main use of porphyrins is to contain iron for hemoglobin. The vast majority of them in the body are used for this task, but they can also hold other metals for other enzymes.

As for what will cure porphyria, I would say our best shot is gene therapy. That is, using a virus or some other means to 'edit' the DNA of a living person and give them a working enzyme to replace the broken one. The reason it's such a difficult to treat problem is its location - one set of cells in one set of organs in an essential biochemical pathway. We can't 'block' the pathway and turn it off, because then where would you get your hemoglobin? We also can't really make it work better, as the enzymes itself are broken. Nor can we manually remove the built up molecules, because they are by and large locked up in the cytoplasm of various cells.

Hope that answered your questions.