J Med Genet: first published as 10.1136/jmg.17.1.1 on 1 February 1980. Downloaded from Review article Journal of Medical Genetics, 1980, 17, 1-14 Haems and chlorophylls: comparison of function and formation G A F HENDRY AND 0 T G JONES From the Department ofBiochemistry, The Medical School, University ofBristol, Bristol BS8 ITD In 1844 Verdeill reported that acid treatment of at the same time by McMunn3 of cytochromes, chlorophyll or haem yielded apparently similar red another group of haem proteins. compounds; he even postulated that chlorophylls It was the demonstration by Nencki and co- would contain iron. Hoppe-Seyler2 confirmed the workers 45 that the degradation of both chlorophylls apparent similarity of acid derivatives of haems and and haems yielded monopyrroles that led them, in chlorophylls from their light absorption charac- true neo-Darwinian fashion, to postulate a common teristics, a point rather overshadowing the discovery origin for animals and plants. 0 0-'I CH2 II copyright. CH CH3 COOH CIH2 CH2 C-O CH2 http://jmg.bmj.com/ NH2 ( CH3' 'CH3 ® 5- Aminolaevulinic acid a CH2 2 1 12 2 CH2 )H COOH CD FIG 1 Structures ofprotohaem and Protoporphyrin IX chlorophyll a and two of their precursors, acid and 5-aminolaevulinic on September 30, 2021 by guest. Protected protoporphyrin IX (with substituent numbering positions). CH2 CH CH.--,j CH2 CH2 COOCH3 Protohoem (haem- b) CooC20H39 Chlorophyll a 1 J Med Genet: first published as 10.1136/jmg.17.1.1 on 1 February 1980. Downloaded from 2 G A F Hendry and 0 T G Jones Following the work ofWillstatter6 and Fischer and particularly those of avian egg shells, have no Stern,7 the structure of most natural and many central complexed metal. There are only five metals unnatural porphyrins was established. Although commonly found in natural porphyrins: copper in a Verdeil's prediction was wrong, he was correct in uroporphyrin III derivative in the flight feather of interpreting chlorophylls and haems as having the tropical Musophagidae family of birds; cobalt as essentially similar structures. the metal component of vitamin B12 (cobalamins)9; Today we can show the similarity between haem iron in the metal complex in haems including and chlorophyll based on their common precursor, haemoglobin, myoglobin, catalase, peroxidases, and protoporphyrin IX (fig 1). The carbon numbering cytochromes. The fourth metal, magnesium, is system used in fig 1 will be used in the subsequent characteristic of all chlorophylls and bacterio- text. chlorophylls. A fifth metal, zinc, may complex enzymically or non-enzymically to many porphyrins Natural occurrence of porphyrins and to the porphyrin breakdown product biliverdin (it is not known if complexing occurs before or after For over a century, scientists have been aware of the ring cleavage). Certainly the ease with which zinc is existence of the numerous types of porphyrin-based inserted non-enzymically into porphyrins in vitro compounds to be found in a wide range ofeukaryotic would make it surprising if zinc porphyrins did not and prokaryotic organisms. It was presumably only exist in vivo. It is indeed more surprising that nature a question of time before reports of extra-terrestrial has confined the metal complexes of porphyrins to porphyrins would be made.8 The earth-bound bio- four or five ions only; chemists have been able to logical porphyrins are diverse and range in colour insert well over 40 metals into porphyrins. from grey-blue (bacteriochlorophyll), green (chloro- The biosynthetic pathway (fig 2) of porphyrins phyll), and red (protohaem) to yellow and brown from the monopyrrole porphobilinogen begins with (avian egg porphyrins). the formation of the cyclic tetrapyrrole uropor- The natural occurrence of many porphyrins is phyrinogen isomers IM and I. Isomers II and IV have shown in fig 2, together with their biosynthetic not been reported in biology; isomer I is not ancopyright. relationships. It will be seen that many tetrapyrroles, intermediate in haem and chlorophyll synthesis, it Porphobil inogen Cu III M bird integuments | Uroporphyrin I Uroporphytrinogen C Turacin http://jmg.bmj.com/ Co feathers -*- CoproporptDhyrinogen III Fe- - --Vitamin B 1Certain bacteria I Avian eggs I hyi I * Sirohoem Plants, fungi, pbacnteria I Harder's gland ___H_rderopo_ in mammals .-Harderopo)rphyrinogen III Zn - egg IAvian eggs Protoporphyrinogen JX- verdin - sm on September 30, 2021 by guest. Protected II F~~~~~~~~~~~~~~~e Haemproteins |Echiuriod (e.g: cotalose) warm harmane Bonellin.s- ? Protohaem -_- Haem b Mg Mot_ rgnim cytochromes Most organisms Protoc hlorophyl l(ide) _,Haem a. c cytochromes Eukaryotic and some prokaryotic Dihydrochlorin a- Haem cl, s --w rProkoryotes | photosynthetic (chlorophylls Icertain fungiI organisms a.b.c.d Leghoemoglobin _| sybosesJPlant-bacteria Hoemoglobin Certain photosynthetic Tetrahydrochlorins [osivrtbrates, bacteria Myoglobin many invertebrates (bacteriochlorophylIs Chlorocruorin a,b.c.d.e ) FIG 2 Biosynthetic pathway oftetrapyrroles and their natural occurrence. Ki-dK k i J Med Genet: first published as 10.1136/jmg.17.1.1 on 1 February 1980. Downloaded from Haems and chlorophylls: comparison offunction andfotrmation rL occurs commonly as an excreted compound in the Anoplura (suckirn lice), and Ixodes (ticks), t1j group of disorders of haem synthesis known as the haemoglobin is derive ftrn the higher a-nalj o t porphyrias. It also occurs in many mollusc shells and and the protein moiety I.d in nutrition. Full re integuments, in just those molluscs which do not of the occurrence of haiei6ilobins and myogtabih synthesise haemoglobin. This led Kennedy10 to in invertebrates are provided by Kennedy.13 The postulate that molluscs themselves may be porphy- following summary is very much a simplification of riacs! These molluscs must additionally make what is a complex story. Haemoglobins have been sufficient isomer III for the synthesis of cytochrome reported in certain protozoan strains, in the larvae prosthetic groups. Uroporphyrin, coproporphyrin, ofthe insect Chironomus, in one sub-class ofmolluscs, and protoporphyrin are found in egg shells and in the bivalvia (Solen, Arca, and Pentunaulus where the some cases account for their characteristic colours. haemoglobin is present in corpuscles), and in one Intermediate between coproporphyrin and proto- gastropod genus Planorbis (as free haemoglobin in porphyrin is harderoporphyrin, which is a pigment the plasma). In the crustacea, haemoglobin appears found in the Harderian gland of the rodent eye, sporadically in all orders of the branchiopods. The though it is present in other tissues. most unusual case occurs in Daphnia, where the A plant equivalent to the porphyric mammal may haemoglobin is generally present in the eggs, but be found in some x-ray or UV treated seedling may be absent in the adult. Many crustaceans also mutants. Some such seedlings accumulate uropor- contain bile pigments, which by analogy with phyrin, coproporphyrin, and particularly proto- mammals are, probably, breakdown products of porphyrin IX. From such findings protoporphyrin protohaem. Among the nemerteans haemoglobin is IX has come to be placed in a central role in the present in some members but not all, published study of haem and chlorophyll metabolism. Proto- phyllogenies showing little correlation with presence porphyrin isomer IX, of the fifteen possible isomers, or absence of haemoglobin. Haemoglobin is more is believed to be a prccursor at the branch point of common in the annelid worms, generally as a freely biosynthesis of both haems and chlorophylls. dispersed pigment. However, in a few species, erythrocyte corpuscles may be found (for example copyright. Naturally occurring iron porphyrins in Travisia and Trevella spp). In the polychaete Aphrodita, haemoglobin is present in the nerve cord. From fig 2 it will be seen that a minor pathway may Among the marine worm phyla, haemoglobin is lead to the iron-chelate sirohaem (see below) and a present in the echiurids and lophophorates, generally major pathway gives rise to a series of haem com- within corpuscles. In that 20th century discovery, the pounds, of which the cytochromes, in one form or deep sea dwelling pogonophora worms, haemoglobin another, are present in nearly all organisms. Haemo- has been reported, but in a freely dispersed form. http://jmg.bmj.com/ globin, a characteristic pigment of vertebrates, is It is towards the top of the invertebrate 'tree', the present in a wide range of organisms. One family of holothurian echinoderms or sea cucumbers, that vertebrates, however, the ice-fish (Chaenicthyidae) discoid cells containing haemoglobin are found, survive in the cold waters of the Antarctic apparently corresponding to the erythrocytes of mammals. without any haemoglobin; their oxygen requirement The monomer myoglobin is closely related in con- is met from oxygen dissolved in blood plasma. formation to one of the chains of the haemoglobin Similarly, the Leptocephalus eel larva has no haemo- tetramer. It is present throughout the vertebrates globin until it reaches the elver stage." A form of but appears only sporadically in the invertebrates. on September 30, 2021 by guest. Protected haemoglobin is found in plants under the name of Typically, myoglobin is present in the gastropod leghaemoglobin, It is, however, confined to those radula muscles and the body wall muscles of various plants which are able to fix nitrogen in co-operation polychaete fanworms and occasionally in other phyla. with the bacterium Rhizobium. Such