THIAMINE 329 



thiamine, biotin, pyridoxine, /?-aminobenzoic acid, pantothenic acid, 

 and inositol (239, 259, 281). Usually, dry weight is the criterion, al- 

 though pyruvic acid formation (93), pigment production (289), and 

 rate of growth on agar (10, 277, 282) have all been proposed. 



Assays based on the dry weight of vitamin-requiring fungi have in 

 general the advantages and disadvantages of any biological assay (171, 

 259). However, the relatively more tedious procedures necessary with 

 the fungi have persuaded most investigators to use, whenever possible, 

 bioassays based on yeast or bacterial growth or metabolism. In special 

 cases, fungi may prove more valuable; thus, different fungi able to use 

 either the pyrimidine or the thiazole moiety of thiamine were used by 

 Krampitz and Wool ley (124) in a study of the thiaminase of carp. 



Bioassays using fungi are critically reviewed by Snell (259); others 

 have been described for biotin (224), pantothenate (290), and thia- 

 mine (93, 289). The Phycomyces assay for thiamine is reviewed by 

 0degard (185). A survey of the response of many fungi to graded doses 

 of water-soluble vitamins (136) brings out some of the difficulties in- 

 herent in biological assay procedures. 



5. THIAMINE 



Thiamine (aneurin, vitamin B x ) is the first vitamin to have been 

 studied as a known entity in the nutrition of fungi, and is the 

 vitamin most frequently required by fungi. Thiamine deficiencies oc- 

 cur in all major taxonomic groups — although the ascomycetes have been 

 less thoroughly investigated than others — and in fungi from many dif- 

 ferent natural environments. 



Reported requirements vary widely (65, 226, 300); time of harvest, 

 temperature, and the composition of the medium can be expected to 

 affect thiamine demand. It seems at least possible that those fungi 

 with very small requirements are able to synthesize thiamine once 

 growth has been initiated. A typical response curve is shown in Fig- 

 ure 1. 



The metabolically active form of thiamine is the pyrophosphate, 

 long known as cocarboxylase because of its coenzyme function in the 

 decarboxylation of pyruvic acid. Thiamine pyrophosphate is also the 

 coenzyme for transketolase and for a variety of enzymatic reactions of 

 a-keto acids (118). In the fungi, its role in the metabolism of pyruvic 

 acid is clear from its acceleration of ethanol formation (42, 247) and 

 the accumulation of pyruvate in thiamine-deficient cultures (64, 93, 

 304). Acceleration of glucose utilization (101) and decrease in oxalate 

 accumulation (175) may operate through the same mechanism. 



