Evolution of Enzymes and the 

 Photosynthetic Apparatus 



MELVIN CALVIN 



Department of Chemistry, University of California, 

 Berkeley, California, U.S.A. 



Mr Chairman, members and guests, I would like to express my thanks to the 

 Organizing Committee for the opportunity to be here, and to congratulate them 

 on the thoroughness and care with which this Symposium has been arranged. 



Time does not allow, nor does this audience require, a summary, or introduc- 

 tion to the present-day conception of various stages which must have occurred 

 in the origin of life on Earth as we know it. The appearance of organic material 

 on the surface of the Earth has already been adequately discussed, and the dis- 

 cussion on the development of cellular organisms will come later. It seemed 

 wiser for me not to attempt even a summary of the paper which appears in the 

 publication of the proceedings of this conference, but rather to select two par- 

 ticular points which I thought might add something to the basic pattern as it 

 has been developed by Oparin. The first of these might be termed the develop- 

 ment of catalysts, that is, enzymes and rudimentary synthetic sequences. The 

 second will be a discussion of the possible mode of the development of what 

 we now know as the photosynthetic apparatus. 



With regard to the first point, the development of catalysts and rudimentary 

 synthetic sequences: Even the most cursory examination of what is now known 

 about the nature of present-day enzymatic mechanisms cannot fail to impress 

 one with the apparent identity between the enzymatic reactions and the reactions 

 as they are known to the organic chemist in the laboratory. For example, gly- 

 oxylase, by which methylglyoxal is converted to lactic acid, is nothing more or 

 less than an internal Cannizzaro reaction which is catalysed by bases. Almost 

 all of the hydrolytic enzyme reactions — esterases, proteases, phosphatases — 

 have their non-enzjmiatic counterpart in the form of generalized acid or base 

 catalysts, or more specialized catalysis by metal salts. For example, again in the 

 case of the phosphatases, the freshly precipitated trivalent metal hydroxides are 

 extremely effective, or manganese ion as a rudimentary phosphotransferase. 



One particular group of catalysts which is widely dispersed in present-day 

 biological systems is that centred around the element iron, particularly catalase, 

 peroxidase and cytochrome. Here, a rather quantitative comparison can be made 

 between the ability of the bare iron atom to perform some catalytic fimction and 

 the ability of the iron atom to perform the same catalytic function as it has been 

 developed in biological systems. Thus, in Fig. i one sees a comparison of the 

 hydrated iron ion, the iron ion surrotmded by a porphyrin as it is in haem, and 



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