96 THE BIOCHEMISTRY OF B VITAMINS 



chemical mechanisms in which they functioned. The goal of the pioneers 

 in the field of vitamin research was to determine the chemical structure 

 of the vitamins so that their syntheses could be effected and preparations 

 made available for the treatment of nutritional deficiency diseases. Also, 

 it was impossible to attack successfully the problem of the mechanisms 

 of vitamin action prior to the time that the multiple nature of vitamin B 

 had been clarified, and before potent concentrates of the individual vita- 

 mins free from other substances having biological activity became 

 generally available. 



Many early investigators of vitamins, particularly those having bio- 

 chemical training and viewpoints, however, recognized that the vitamins 

 must act as "catalysts," since only minute amounts were needed to pro- 

 duce such profound changes in biological systems; but the nature of the 

 "catalytic activity," of course, at that time could not be explained. 



Fortunately, the study of enzymes and enzyme activity was proceeding 

 simultaneously with the development of the nutritional sciences. It is 

 interesting to note that 1926 was an epochal year in both fields, for it 

 marked the isolation for the first time of a vitamin in crystalline form 

 (thiamine from rice bran) 1 and the first isolation of an enzyme (crystal- 

 line urease from jack bean meal). 2 These two accomplishments offered 

 irrefutable evidence that the activity of both vitamins and enzymes 

 could, at least in some cases, be attributed to specific chemical compounds. 

 Previous to this date some scientists had speculated on the relationship 

 between enzymes and vitamins, and had pointed out that one of the most 

 likely means by which the vitamins could exert their "catalytic activity" 

 was to participate in some way in enzymatic reactions. It is probably 

 difficult for the younger scientists of today, who have always thought of 

 the vitamins and enzymes as specific chemical entities and who in their 

 training have always associated vitamin activity with enzyme action, to 

 realize that twenty-five years ago explaining a vitamin function in terms 

 of enzymes was only a conjecture, and that even fifteen years ago the 

 hypothesis that a B vitamin functioned directly in a biochemical reaction 

 had yet to be demonstrated. 



The actual proof that a B vitamin is an integral part of an enzymatic 

 reaction was not made until 1935, when a component of the "yellow 

 enzyme" was identified as riboflavin (a substance whose status as a 

 vitamin at that time was debatable) . 3 Two years later an essential part 

 of the enzyme system required for the biological decarboxylation of 

 pyruvic acid was shown to be a derivative of thiamine. 4 By 1935 nicotina- 

 mide had been identified as a part of molecules essential for reac- 

 tions taking place when glucose is utilized by erythrocytes and yeast, 5 



