280 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



cules of the substrate, and the turnstiles are the active centers of the 

 enzyme which transform fans into spectators one at a time. As long 

 as there are enough people to keep the turnstiles going at full speed, 

 the rate of change of fans into spectators will be constant and inde- 

 pendent of the length of the queues; but if only a few people ap- 

 proach, they will go in without waiting and the rate of conversion 

 of fans will be directly proportional to the number arriving at the 

 ground. One might extend the analogy by comparing certain vita- 

 mins to the oil necessary to lubricate the turnstile mechanism. If 

 this is lacking, the turnstile will seize up and chaos result. 



The number of different enzymes already known is very large, and 

 new ones are constantly being found. The discovery of penicillin 



CONCENTRATION OF SUBSTRATE OR 

 NUMBER OF FANS ARRIVING PER 

 MINUTE AT THE GROUND. 



Figure 2. — Relationship between rate of enzynaatic reaction and the substrate concentra- 

 tion. A similar curve would be obtained by plotting the rate of the "football crowd" 

 reaction and rate of arrival of fans mentioned in the text. 



was followed very quickly by the discovery of penicillinase, the en- 

 zyme which destroys it. 



Every species of plant and animal seems to possess its own set of 

 enzymes which do not correspond exactly to similar enzymes present 

 in other species, so that the total number of individual enzymes may 

 run into many millions. Innumerable compounds occur naturally 

 ill plants and animals and for each there must exist enzymes which 

 can make and break it down. Enzymes enable living organisms 

 to carry out a great variety of reactions in dilute aqueous solution 

 at temperatures between freezing point and blood heat; there is no 

 need for extremes of acidity or alkalinity. Without using enzymes, 

 the organic chemist can carry out only some of these changes, and then 

 often he may have to use higher temperatures, corrosive reagents 

 and concentrated reagents, and sometimes to exclude water completely. 



