De Duve

However, there are also biogenesis models which do not require phosphate, such as the inorganic hypothesis of the origin of life proposed by Cairns-Smith (see Sect. 7.1), the thioester world proposed by de Duve (see Sect. 7.4) or the sulphur-iron world suggested by Wachtershauser (see Sect. 7.3). The RNA world (see Chap. 6), however, cannot exist without phosphate. 

The often posed question as to whether phosphorus compounds were active in the initial phases of the development of life, or intervened only at a later stage in the evolutionary process, remains unanswered. However, de Duve (1991) was completely right when he stated that life is basically organized around phosphorus . 

The still open question, Information or metabolism first has again been discussed by Robert Shapiro. In an article with the title Did This Molecule Start Life A Simple Origin for Life , he again stresses that it is improbable that life could have begun in an RNA world (referred to here as RNA-first ). Shapiro offers his own suggestion in the metabolism debate he assumes that cyclical processes, occurring in small compartments, lead from small molecules to systems of higher complexity. The Shapiro model takes into account aspects of the approaches and hypotheses proposed by Wachtershauser (see Sect. 7.3), de Duve (see Sect. 7.4) and Kauffmann (see Sect. 9.3). In order to avoid one-sidedness, Shapiro s article is accompanied by a short reply An RNA-First Researcher Replies . In this way, the reader is shown in a clear and understandable manner what the differences between the two approaches are (Shapiro, 2007). 

About three years after Wachtershauser s first publication appeared, an article by Christian de Duve and Stanley Miller was published in the Proceedings of the National Academy of Sciences under the title Two-Dimensional Life the title alluded to the theory of reactions at positively charged pyrite surfaces (de Duve and Miller, 1991). Their criticisms of the chemoautotrophic theory were directed particularly towards certain kinetic and thermodynamic aspects, but also to theoretical statements for which no experimental support was available. 

The discovery of the deep sea hydrothermal systems, and the sulphur-metabolising bacteria which live in them, caused some researchers to look more closely at the element sulphur. It seemed obvious to consider a link between sulphur bacteria— primitive life forms—and the emergence of the simplest forms of life, de Duve, 1974 Nobel Prize winner for medicine, joined the ranks of the biogenesis researchers in the 1980s. 

The physiologist de Duve concentrated his efforts on a material link between the prebiotic phase of the primeval Earth and the state of development at which RNA (or a similar type of molecule) determined the further progress of the evolution process. In particular, this connecting link needed to have been able to transfer chemical energy, since without such a procedure, the RNA synthesis appears impossible. The molecular species which Christian de Duve favours for this important function is that of the thioesters. The exact reasoning as to why this is the case is discussed in detail in his book Vital Dust Life As a Cosmic Imperative (de Duve, 1996). 

The thioester world postulated by de Duve should in fact be called the sulphur-iron world , since iron ions are essential for the redox processes occurring in such a thioester world, de Duve (1991, 1996) asks a question which is vital for the whole of prebiotic chemistry where did the redox equivalents necessary for the construction of biomolecules on the primeval Earth come from This question becomes largely irrelevant if the strongly reducing atmosphere postulated by Miller/Urey and... 

De Duve (and other authors) consider the source to be iron, which as Fe2+ provides one electron per Fe atom when subject to solar UV irradiation. The Fe3+ generated can be precipitated from solution with Fe2+ as a mixed oxide (FeO Fe2C>3 = FesOzt). This is found today in the form of black-band ironstone, an ore which is between 1.5 and 3.5 billion years old and was produced by interaction of Fe2+ with oxygen produced by light-converting bacteria. (The figure of 3.5 billion years is, however, not accepted by some scientists see Sect. 10.1). 

How could this problem be solved Only traces of thioesters are formed from free carboxylic acid and thiols in aqueous solution, i.e., the equilibrium reaction 7.15 is shifted to the left. According to de Duve (1991), there are two possibilities for spontaneous thioester synthesis under conditions present on the primeval Earth ... 

Fig. 7.8 Two examples of important reactions in the thioester world a the phosphorolysis of thioesters leads to acylphosphates and b a-ketoadds are formed in the reductive cleavage of thioesters with accompanying carbonylation (de Duve, 1991)...

According to de Duve, thioesters on the young Earth were capable of a broad spectrum of chemical reactions for example, of phosphorolysis leading to acylphos-phates (Fig. 7.8a) or of reductive thioester cleavage, which (after carbonylation) made possible the synthesis of ketoacids (Fig. 7.8b). 

Compounds of crucial importance for the RNA world or a precursor phase could have been formed in this or similar ways. Thus, a thioester world seems to support the RNA world hypothesis, although de Duve can be considered as a careful critic of the latter hypothesis. His opinions were expressed in a short article in Nature under the provoking title Did God make RNA (de Duve, 1988). 

The thioester hypothesis can be summed up as follows the formation of thiols was possible, for example, in volcanic environments (either above ground or submarine). Carboxylic acids and their derivatives were either formed in abiotic syntheses or arrived on Earth from outer space. The carboxylic acids reacted under favourable conditions with thiols (i.e., Fe redox processes due to the sun s influence, at optimal temperatures and pH values) to give energy-rich thioesters, from which polymers were formed these in turn (in part) formed membranes. Some of the thioesters then reacted with inorganic phosphate (Pi) to give diphosphate (PPi). Transphosphorylations led to various phosphate esters. AMP and other nucleoside monophosphates reacted with diphosphate to give the nucleoside triphosphates, and thus the RNA world (de Duve, 1998). In contrast to Gilbert s RNA world, the de Duve model represents an RNA world which was either supported by the thioester world, or even only made possible by it. 

BruB D and Leusch G (Eds.) (2006) Lectures on Quantum Information. John Wiley Sons Ltd. Copley SD, Smith E, Morowitz HJ (2005) Proc Natl Acad Sci USA 102 4442 de Duve C (1991) Blueprint for a cell The Nature and the Origin of Life, Carolina Biological Supply Company... 

Careful examination of the yellowish sediment obtained after spinning down the crude mitochondrial fraction showed it was frequently overlaid with loosely packed, fluffy material —the fluffy layer. Experiments from de Duve s and, later, Novikoff s laboratories in the 1950s demonstrated that the lighter, lysosomal fraction was enriched in a number of hydrolases including acid phosphatase, aryl sulphatase, B glucuronidase, RNAase, and a peptidase, cathepsin. All the enzymes had optimal pHs in the acid range (pH 5-pH 6). Density... 

As Christian de Duve has put it Ah biological expenditures are, in the last analysis, supported by the hydrolysis of ATP to ADP and inorganic phosphate, one of the most noteworthy singularities offered by hfe today. ... 

The de Duve quotation is taken from C. de Duve, Singularities Landmarks on the Pathways of Life, Cambridge University Press, New York, 2005. 

De Duve, C. (1965). The separation and characterization of sub cellular particles. Harvey Lectures 59,49-87. 

The bibliography on Duchamp is vast. There are also many specific works treating his relationship to alchemy or dematerialization (that is, Duchamp as the first conceptual artist). De Duve and Krauss are particularly helpful in summarizing the primary issues. 

De Duve, Thierry. Joseph Beuys, or Last of the Proletarians. October ys, (Summer 1988) 47-62. 

De Duve, Thierry, and Rosalind Krauss. Echoes of the Readymade Gritique of Pure Modernism. October jo (The Duchamp Effect) (Autumn 1994) 60—97. 

What follows is quoted as transcribed in de Duve, Definitively Unfinished MD, 69-82, 463. 

For the most complete, although still highly speculative, study of this mysterious sojourn in the Bavarian capital, see T. de Duve, Resonances of Duchamp s Visit to Munich, in Kuenzli and Naumann, 41-63 (this is a translation of the fifth chapter of Duve, Nominalisme pictural). See also the essay by Veit Loers, Miinchens okkultisches Netzwerk, in Loers, 238-80. 

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