44 



LIFE: ITS BEGINNINGS AND NATURE 



had of the number and variety of enzymes 

 present in protoplasm, consider for a mo- 

 ment the burning of gkicose to CO2 and 

 H2O. This can be done in a test tube, pro- 

 viding external heat is applied, much more 

 than could be tolerated in an animal body. 

 However, this reaction proceeds speedily 

 and without any marked temperature ele- 

 vation in protoplasm. The impressive thing 

 about this apparently simple process is that 

 there are at least 25 steps involved in this 

 oxidation, and probably a different enzyme 

 is participating in each step. The glucose is 

 broken down step by step, each enzyme 

 contributing its part in the proper order. 

 Furthermore, each enzyme involved in 

 every step is specific for that step. It does 

 that one job alone, and no other. Their 

 specific action reminds one of union work- 

 ers, each doing his own job and no other. 

 Think of the myriad enzymes that must be 

 present in protoplasm to make life possible. 



The analysis of over 30 enzymes up to 

 the present indicates they are protein in 

 nature. The first one, urease, was crystal- 

 lized in 1926; many others have been pro- 

 duced in pure form since. In general, an 

 enzyme can accelerate a reaction in either 

 direction, that is, its action is reversible. 

 Experimentally, however, it is much easier 

 to demonstrate the activity of enzymes that 

 bring about exothermic reactions which lib- 

 erate energy, than endothermic reactions 

 which store energy. Theoretically, enzymes 

 that break down a glucose molecule should 

 be able to reconstruct the molecule, pro- 

 viding energy is supplied from the outside. 

 This may be true, but it is difficult to prove 

 because an exothermic reaction is required 

 to supply the energy needed for the recon- 

 struction at the same time as the endother- 

 mic reaction is going on. It is impossible 

 to observe them simultaneously. These 

 coupled reactions must always proceed syn- 

 chronously and since they are locked up 

 within the cell, they are extremely difficult 

 to observe. 



The activity of enzymes is controlled by 



the movement of molecules just as all chem- 

 ical reactions are. As the temperature rises 

 from to 40 degrees Centigrade, enzyme 

 action increases; with each 10 degree rise 

 in temperature the action doubles, up to 

 a critical temperature of about 40 degrees 

 where all activity ceases. It is interesting 

 to observe that cold-blooded animals 

 (called poikilothermal, that is, those that 

 cannot maintain a constant body tempera- 

 ture, such as insects, frogs, and lizards ) are 

 forced into hibernation because at reduced 

 body temperatures enzymatic activity is 

 slowed to a point where normal response 

 is impossible. Warm-blooded animals 

 (called monothermal, that is, birds and 

 mammals ) are not bothered in this respect 

 because their bodies maintain a constant 

 temperature. It is not sheer coincidence 

 that the body temperature of these animals 

 happens to be the point of optimal activity 

 of the body enzymes. 



Enzymes are particularly sensitive to hy- 

 drogen and hydroxyl ions, as well as certain 

 other specific ions such as calcium. Diges- 

 tive enzymes do their best work in solutions 

 with the proper number of hydrogen and 

 hydroxyl ions. Ptyalin in the mouth acts 

 best at or near neutrality, whereas pepsin 

 in the stomach requires a strong acid solu- 

 tion for optimal activity. Trypsin in the 

 small intestine needs a slightly alkaline me- 

 dium to do its best work. 



Enzvme chemistiy is an active field of 

 research today and it is hoped that much 

 more will be learned in the next few years 

 about hoiv enzymes work. 



Coenzymes. Intimately linked with intra- 

 cellular enzymes are certain simpler organic 

 compounds which are essential in certain 

 vital metabolic processes in protoplasm. 

 These non-protein molecules are called co- 

 enzymes. They are so associated with cer- 

 tain enzymes that neither is effective without 

 the other. Vitamin Bi is a coeiirzyme which 

 is essential for the operation of several oxi- 

 dizing enzymes in both plants and animals. 

 Strangely enough, animals are unable to 



