Pigments of Life

This IS used for synthesis of porphobilinogen fEq 10 24 Porphobilinogen is the key building block in the biosynthesis of pigments of life such as porphyrins, heme, and vitamin Interestmg application of porphobdiogen to synthesis of immunocomponents for the measurement of lead fPb by fluorescence polarizadon Immunoassay has been reported "... 

E. McDonald, Biosynthesis of the pigments of life Formation of the macrocycle. Nature 285 17, 1980. This paper discusses the steps in tetrapyrrole biosynthesis and the pathways diverting this nucleus to chlorophylls, hemes, cytochromes, and other macrocyclic pigments. 

The porphyrins are called pigments of life and occur broadly in nature. They fulfill many roles ranging from oxygen transportation (hemoglobin), electron transfer (cytochromes), oxidations and reductions (peroxidase, catalase, cytochrome, oxi-... 

Battersby AR How nature builds the pigments of life the conquest of vitamin B12. Science 264 1551-1557,1994. 

Fig. 2.5 The six main typ>es of pigments of life derived from uroporphyrinogen III.

A careful look at the main "pigments of life" (as Professor Sir Alan Battersby from the University of Cambridge calls them), e.g. heme, chlorophyll, bacterio-chlorophyll, and vitamin Bi2, shows that they have several features in common. They all consist of four pyrrole-type rings, with a greater or lesser degree of unsaturation (depending on the macrocycle), and they have a rather unusual pattern of substituents on their peripheral p-carbons. 

This brings us to the question of why the t)rpe III isomer, of the four possible uro gen isomers, is the one chosen by nature from which to construct the pigments of life. Some clues to the answer can be found in the way that PBG combines with itself under non-enzymatic (and anaerobic) conditions, and what happens to the porphyrinogens under the influence of acid. 

Eschenmoser went on to demonstrate how it would be possible to generate the simplest chromophore type, the Fe(II) complex of sirohydrochlorin (the cofactor of nitrite and sulphite reductase), from glycine nitrile in a reaction sequence consisting of only five steps. The main conclusion that Eschenmoser comes to is that the arrangement of acetic and propionic acid side chains around the periphery of the pigments of life (i.e. the type III arrangement) corresponds to the thermodynamically favoured structure type. It has to be borne in mind that for this to happen (and presumably for there to be large amounts of porphyrins and other tetrapyrroles available as prebiotic... 

Barker HA and Lipmann F (1949) The role of phosphate in the metabolism of Propionibacterium pentosaceum. JBiol Chem 179 247-257 Barksdale L (1970) Corynebacterium diphtheria and its relatives. Bacteriol Rev 34 378-422 Battersby AR (1985) Biosynthesis of the pigments of hfe. Proc R Soc Lond B 225 1-26 Battersby AR (1994) How nature builds the pigments of life the conquest of vitamin B. Science 264 1551-1557... 

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