282 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1951 



Anything that can inhibit or stop vital enzymes from functioning 

 smoothly in the organism may lead to its death. The absence of 

 certain vitamins is one example already mentioned. Heat and ultra- 

 violet light may produce irreversible changes in the protein mole- 

 cule, and if this protein is an enzyme, loss of activity results. 

 Another way in which an enzyme may be inhibited is by some com- 

 pound reacting chemically with it or forming a stable complex at 

 the active center, which is then blocked and cannot fulfill its normal 

 role any longer. One fat man firmly wedged in the turnstile might 

 stop the "football crowd" reaction. 



The highly poisonous nature of some compounds has been correlated 

 with their ability to "knock out" certain important enzymes, so that 

 only a small amount of such poisons may be necessary to produce very 

 serious effects on the well-being of the whole organism. One part of 

 mercuric chloride in 200 million parts of solution will reduce by half 

 the efficiency of the enzyme catalase. Cyanide is very efficient at stop- 

 ping the working of some of the enzymes concerned with oxidation 

 while some of the highly toxic phosphorus insecticides are extremely 

 potent inhibitors of cholinesterases (enzymes that play an essential 

 part in the working of the nervous system of higher animals, and 

 probably also of insects) . 



The existence of antienzymes in living systems has been demon- 

 strated. Olie of the best examples is shown by the roundworm, 

 Ascaris, which lives in the animal intestine and escapes being digested 

 by the enzymes present by producing specific enzymes that neutralize 

 the effect of specific digestive enzymes. However, if the worms are 

 placed in dilute solutions of digestive enzymes from plants (such as 

 ficin from the latex of certain fig trees) , they are digested alive as they 

 lack specific inhibitors to these unfamiliar enzymes. 



An intriguing problem is why digestive enzymes do not attack and 

 digest the glands producing them, or the intestinal tract into which 

 they are secreted. One reason may be that such enzymes are usually 

 secreted in an inactive form, and the active center is "uncovered" later. 

 The pancreas secretes trypsinogen, which is inactive but is converted 

 into active trypsin in the intestines. The stomach secretes a mucilage 

 that coats its walls and probably protects them from the action of 

 the digestive juice. 



When biochemical processes are examined in detail, it is often found 

 that a change, such as the fermentation of sugar or the oxidation of 

 acetic acid to carbon dioxide and water, is not achieved by a single 

 enzyme but by a whole battery of them. There may be a dozen or 

 more stages, each brought about by a separate enzyme. The substrate 

 has therefore to move from one enzyme to another, and at each stage 



