44 J. D. BERNAL 



efficiency of the reaction, implying an adjusted set of quantum states for the 

 more active agent in the transformation, and minimizing the activation energy. 

 These functions we know today as those of enzyme and co-enzyme respectively. 

 The first of these are now provided by the proteins, the second by nucleotides, 

 flavones and some transition-metal compounds. It is most significant that, while 

 the enzymes are so far innumerable, each responsible for one or two reactions 

 only, the co-enzymes are few and each can function in many different reactions. 

 Specificity in quantum level of the active partner would seem to be less important 

 than specificity in spatial configuration in the passive partner. 



The prevalence of nucleotides among co-enzymes is particularly noteworthy. 

 The active group here is the terminal phosphate which can add one or two 

 further phosphate groups that are easily detachable by a process of energy 

 exchange, long known to biochemists as the energy-rich phosphate bond. In 

 existing life and probably in life as far back as we can trace it the sugar-purine 

 complex has been attached to the phosphate group. But this probably indicates 

 a limiting stage of efficient modification of quantum levels. At an earher stage, 

 before sugars or purines had been synthesized, the basic phosphate-hydrogen 

 exchange mechanisms had probably been active first as oHgo- or poly-meta- 

 phosphate and then with phosphate Hnked with some simple carbon-nitrogen 

 derivative such as cyanate. Indeed, as Lipmann claims [14], carbamyl phosphate 

 (OC-NH2*OP03) derived from the cyanate and phosphate ions can reasonably 

 be regarded as the first Uving molecule, or at least as the first step in the evolu- 

 tion of biochemistry. 



The association of phosphate with the fixing of carbon dioxide may be related 

 to the basic anabolic process, the formation of amino acids and sugars at first 

 in the triose glyceraldehyde form. The energy required for this came in the 

 first place from dehydrogenation reactions, but at some stage it came to be 

 derived from sunlight by photochemical reactions. The present highly efficient 

 mechanism of photosynthesis is too comphcated to have been an early one, but 

 its place may have been filled first by some other and less efficient organo-metallic 

 light trap, perhaps a clathrate compound of iron. The origin of the first effective 

 photosynthesis, and with it the first production of molecular oxygen and its 

 concentration in the atmosphere, may also be linked with that of the bulk pro- 

 duction of pentose and hexose sugars. The earher this occurred in biopoesis the 

 earher can have been the origin of the new omnipresent nucleosides. 



Papers presented at the Symposium, notably those of Calvin, Krasnovskii, 

 Reid and Sorokin, have enhghtened me on the evolution of photosynthesis by 

 emphasizing the separation of at least three factors existing in the photosynthesis 

 of green plants : carbon dioxide fixation, hght energy utilization, and oxygen 

 production. These may well have originated separately. Carbon dioxide fixation 

 using some other source of free energy I had already postulated as preceding 

 photosynthesis. However, I had not considered the intermediate stage, which I 

 now feel fits much better into the picture of photosynthetic decomposition, of 

 SH groups giving molecular sulphur as now carried out by the sulphur bacteria. 



This would have had the first effect of photosynthesis in biopoesis in providing 

 a secure source of organic materials, perhaps even too much in the absence of 



