D. E. GREEN 



The problem of the autocatalysis of genes is essentially similar 

 to that of viruses. What is the starting material for the synthesis and 

 how is the synthesis accomplished? No concrete answer is possible 

 as yet, but there are indications that the solution to the problem will 

 be in terms of enzyme chemistry. One intriguing development in 

 recent years has been the successful application of the concept of com- 

 petitive inhibition drawn from the field of enzymes to the virus problem. 

 Two strains of the same virus are found to antagonize one another's 

 growth in the same host, presumably by competing for the same 

 pabulum. In chemotherapy, two substrates, one natural, the other 

 "fraudulent," compete for the same enzyme. In the example above, 

 two viruses are made to compete for the same substrate. This virus 

 interference phenomenon occurs only when the two strains are closely 

 related, just as competitive inhibition occurs only when the 

 "fraudulent" substrate closely resembles the natural. 



The past decade has seen not only the extension of our knowl- 

 edge of enzymes to other fields of biochemistry and medicine but also 

 the extension in part of the enzyme concept to noncatalytic proteins. 

 Let us compare, for example, two proteins, catalase and hemoglobin. 

 Both contain iron protoporphyrin as prosthetic group and both are 

 highly specific. Catalase catalyzes the decomposition of hydrogen 

 peroxide into oxygen and water, whereas hemoglobin combines re- 

 versibly with molecular oxygen. Catalase cannot function as hemo- 

 globin and conversely hemoglobin for all practical purposes does not 

 catalyze the decomposition of hydrogen peroxide. Catalase forms a 

 compound with hydrogen peroxide and then the enzyme-substrate 

 compound undergoes decomposition. This cyclical process repeats 

 itself more than two million times per minute at 0°. In a similar way, 

 hemoglobin forms a compound with molecular oxygen over a certain 

 range of oxygen tension, and the complex is dissociable by lowering 

 the oxygen tension. The speed of the combination is of about the same 

 order of magnitude as for the combination of catalase with hydrogen 

 peroxide. This comparison is not being made to infer that hemoglobin 

 is an enzyme. There is little to be gained by a redefinition of the 

 classical concept of an enzyme to include a proteinlike hemoglobin, 

 because after all there is a real distinction between a catalyzed reaction 

 and a noncatalyzed reaction. However, it is important to recognize 

 the many properties in common which catalase and hemoglobin share. 



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