Thermal Factors in Archaeometabolism 



s. SCHER 

 Department of Botany, Rutgers University, New Brunswick, New Jersey, U.S.A.* 



One of the more formidable problems of comparative biochemistry is to deter- 

 mine the nature of the first enzymes in primitive metabolic systems. Tracing the 

 course of complex enzyme systems in present-day organisms to their begin- 

 nings poses several interesting questions. Do present-day forms contain primitive 

 enzymes? Bernai [i] has suggested that everything an organism contains is 

 evidence of its predecessors ; and to get significant information we must draw 

 deductions from the chemical structure of actual organisms. If we were to look 

 for archaic enzymes in present-day organisms how would we recognize them? 

 To put this question in another form, what would be the best criteria for primi- 

 tive versus advanced or recent enzymes ? According to Oparin [2], the primitive 

 pattern of metabolism has been masked by a superstructure of supporting or 

 alternate pathways. How then are we to differentiate the first enzymes from those 

 which have developed later in the course of evolution ? 



If we take as postulates that Ufe arose in thermal waters and that the evolution 

 from heterotrophy to autotrophy was paralleled by a gradual decrease in en- 

 vironmental temperature, then thermal factors may provide clues to the nature 

 of primitive metaboUc systems. 



In support of a thermal origin of life, Copeland [3] has provided taxonomic 

 evidence which suggests that the thermophihc blue-green algae are a vestige of 

 a primordial thermal flora, and that the thermophihc forms have given rise to 

 the mesophihc forms. All of the orders, most of the families and the majority of 

 the important genera of the blue-green algae include thermal species. Their 

 notable incidence in thermal habitats suggests the probability of the origin of 

 hving organisms in general in thermal waters. 



Haldane [4] postulated that the most primitive metabohc systems were hetero- 

 trophic, with little or no synthetic ability. The metabohc activity of such a unit 

 was at first completely dependent upon its environment. Fox [5] has found that 

 heat-induced anabolic reactions follow the same sequence, and produce the same 

 intermediates as occur in present-day living systems. In addition, Abelson [6] 

 has demonstrated the stabihty of certain amino acids at temperatures above 

 those in thermal waters. 



If biochemistry recapitulates pyrochemistry, as suggested by Fox, then it may 

 be assumed that with the coohng of the Earth, the efficiency of pyrosynthesis 

 would be reduced. This would result in the depletion of one or more inter- 



* Present address: Hopkins Marine Station of Stanford University, Pacific Grove, 

 California. 



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