What Are Porphyrins?

Porphyrins are a class of macrocyclic heterocyclic compounds formed by the interconnection of the -carbon atoms of four pyrrole-like subunits through a methine bridge (= CH-).

Overview

Porphyrin (pronunciation: b lín) porphyrin (s) is a class of four pyrrole subunits

Porphine derivatives

Porphine is a precursor, and a molecule of porphin combines with a metal ion to form a porphyrin. Porphyrins and their derived compounds are widely present in organisms and important organelles related to energy transfer. For example, heme is an iron-containing porphyrin compound, chlorophyll is a magnesium-containing porphyrin compound, vitamin B12 is a cobalt-containing porphyrin compound, and they all have important physiological functions in the body. In animals, it is mainly found in heme (iron porphyrin) and hemocyanin (copper porphyrin). In plants, it is mainly found in vitamin B12 (cobalt porphyrin) and chlorophyll (magnesium porphyrin). It is a blood cell carrying oxygen Carrying respiration and the key role of plant cells during light and action. Therefore, it has aroused great interest from chemists and biologists. It is believed that porphyrins have an excellent or even magical role in energy transfer. However, porphyrins are also prone to combine with other substances in the body for some reasons and cause porphyria, manifested as dermatitis, ringworm, senile plaques, etc. Porphyrin compounds have great applications in various fields such as polymer materials, chemical catalysis, electroluminescent materials, and molecular targeted drugs. The research interest in porphyrins in the world's scientific community and even in the chemical engineering community is increasing year by year.

Porphyrin compounds are widely present in geological bodies such as petroleum and asphalt in different ages and different genesis.

Meaning in the origin of life

The porphyrin ring is the core and soul of chlorophyll, a photosynthetic pigment molecule. It is its unique sensitivity that lights up the light of life. This magic ring can not only sense photons but also transfer electrons. It is such a feature that makes it indispensable not only in photosynthetic organisms but in almost all other life forms.

Two facts strongly suggest the homology between cytochrome's heme and chlorophyll. The first is the high similarity of the two in the core structure (the former is iron porphyrin and the latter is magnesium porphyrin), and the second is the similarity between the two biosynthetic pathways in existing organisms. Several identical intermediates. Cytochrome C mutates quite slowly: there is a one-letter change every 25 million years, while other proteins such as fibrin change every 600,000 years or so, which is more than 40 times faster than cytochrome C. For biological survival, the more core processes may be more conservative in evolution, the more natural selection will not tolerate large changes, and cytochromes are such important molecules.

Biosynthetic pathway from ALA to heme

Heme can be regarded as a derivative of chlorophyll. The photochemical reaction center with chlorophyll as the core has been continuously selected, developed and optimized in the origin of photosynthesis. Some chlorophyll molecules have evolved into heme, which are assumed by different nodes in the electron transfer chain Role (should be a combination determined by membrane structure, redox potential, etc., although somewhat random), and some have evolved into prosthetic groups like F430 in methanogens. The diverse heme molecules are so successful that they have become necessary for the electron transport chain of non-photosynthetic bacteria. Therefore, heme may have evolved from the ancient photosynthetic molecule, chlorophyll, and it has since become an essential component of the electron transport chain of all life groups, which can be considered as strong evidence for the origin of photosynthesis in life.

The structural similarity between chlorophyll and heme prosthetic group of cytochrome is shown in the figure below. Decyclization (red marked position) occurred during the transition from magnesium porphyrin to iron porphyrin. Historically, membrane-coupled chlorophyll molecules may have been formed by the addition of a phospholipid to a porphyrin ring. Blue dotted lines with arrows indicate possible evolutionary directions. ^[2]

Comparison of the structure of heme prosthetic group of chlorophyll and cytochrome