Protoporphyrins are tetrapyrroles containing the following side chain

Side chain

In organic chemistry and biochemistry, a side chain is a chemical group that is attached to a core part of the molecule called "main chain" or backbone. The placeholder R is often used as a generic placeholder for alkyl group side chains in chemical structure diagrams. To indicate other non-carbon...

s:

• methyl (4)
• propionic acid
  Propionic acid
  Propanoic acid is a naturally occurring carboxylic acid with chemical formula CH3CH2COOH. It is a clear liquid with a pungent odor...
  
   (2)
• vinyl
  Vinyl
  A vinyl compound is any organic compound that contains a vinyl group ,which are derivatives of ethene, CH2=CH2, with one hydrogen atom replaced with some other group...
  
   (2)

Protoporphyrin IX

Protoporphyrin IX

Protoporphyrin IX, in the metabolism of porphyrin, is created by the enzyme protoporphyrinogen oxidase.-Heme b biosynthesis:In heme biosynthesis, the enzyme ferrochelatase converts it into heme b Protoporphyrin IX, in the metabolism of porphyrin, is created by the enzyme protoporphyrinogen...

 is a biochemically widely used carrier molecule for divalent cations. Together with iron (Fe 2+) the body of the heme

Heme

A heme or haem is a prosthetic group that consists of an iron atom contained in the center of a large heterocyclic organic ring called a porphyrin. Not all porphyrins contain iron, but a substantial fraction of porphyrin-containing metalloproteins have heme as their prosthetic group; these are...

- group of hemoglobin

Hemoglobin

Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...

, myoglobin

Myoglobin

Myoglobin is an iron- and oxygen-binding protein found in the muscle tissue of vertebrates in general and in almost all mammals. It is related to hemoglobin, which is the iron- and oxygen-binding protein in blood, specifically in the red blood cells. The only time myoglobin is found in the...

 and many other heme-containing enzymes like cytochrome c and catalase

Catalase

Catalase is a common enzyme found in nearly all living organisms that are exposed to oxygen, where it catalyzes the decomposition of hydrogen peroxide to water and oxygen...

 are formed. Complexed with magnesium-ions (Mg 2+) the main part of the Chlorophylls are formed. Complexed with zinc-ions (Zn 2+) it forms Zinc protoporphyrin

Zinc protoporphyrin

Zinc protoporphyrin is a compound found in red blood cells when heme production is inhibited by lead and/or by lack of iron. Instead of incorporating a ferrous ion, to form heme, protoporphyrin IX, the immediate precursor of heme, incorporates a zinc ion, forming ZPP...

.

The number (e.g. IX) indicates the position of different side chains, but historically, as the nomenclature has grown, it has done so systematically only in parts.

Protoporphyrin IX as a direct precursor of heme is accumulated by patients of erythropoietic protoporphyria

Erythropoietic protoporphyria

Erythropoietic protoporphyria is a relatively mild form of porphyria, although very painful, which arises from a deficiency in the enzyme ferrochelatase, leading to abnormally high levels of protoporphyrin in the tissue...

, which is one of the genetic disorders of the biosynthesis of the heme -pathway. It causes a severe photosensivity against visible light.

The sensitivity of protoporphyrin IX against light is also used as a therapy against different forms of cancer (photodynamic therapy

Photodynamic therapy

Photodynamic therapy is used clinically to treat a wide range of medical conditions, including malignant cancers, and is recognised as a treatment strategy which is both minimally invasive and minimally toxic...

, PDT).

Protoporphyrins are deposited in the shells of the eggs

Egg (biology)

An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...

 of some bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s as a brown or red pigment, either as a ground colour or as spotting. This occurs in most passerine

Passerine

A passerine is a bird of the order Passeriformes, which includes more than half of all bird species. Sometimes known as perching birds or, less accurately, as songbirds, the passerines form one of the most diverse terrestrial vertebrate orders: with over 5,000 identified species, it has roughly...

 species, some ground-nesting non-passerines, such as wader

Wader

Waders, called shorebirds in North America , are members of the order Charadriiformes, excluding the more marine web-footed seabird groups. The latter are the skuas , gulls , terns , skimmers , and auks...

s, gull

Gull

Gulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...

s, nightjar

Nightjar

Nightjars are medium-sized nocturnal or crepuscular birds with long wings, short legs and very short bills. They are sometimes referred to as goatsuckers from the mistaken belief that they suck milk from goats . Some New World species are named as nighthawks...

s and sandgrouse

Sandgrouse

The sandgrouse are a family, Pteroclididae, of 16 bird species, the only living members of the order Pteroclidiformes. They are restricted to treeless open country in the Old World, such as plains and semi-deserts. They are distributed across northern, southern and eastern Africa as well as...

, where it provides camouflage, and some parasitic

Brood parasite

Brood parasites are organisms that use the strategy of brood parasitism, a kind of kleptoparasitism found among birds, fish or insects, involving the manipulation and use of host individuals either of the same or different species to raise the young of the brood-parasite...

 cuckoo

Cuckoo

The cuckoos are a family, Cuculidae, of near passerine birds. The order Cuculiformes, in addition to the cuckoos, also includes the turacos . Some zoologists and taxonomists have also included the unique Hoatzin in the Cuculiformes, but its taxonomy remains in dispute...

s, which need to mimic their passerine hosts' eggs.

Protoporphyrins strengthen the egg shell, and are deposited where the shell is too thin as a result of calcium shortage. Spotting therefore tend to be heavier where the local soil is calcium-deficient, and in the eggs laid last in a clutch.