232 



PHYHIOLOGY OF THE FUNGI 



thiamine (Wilson and Harris, 1949). Pyrithiamine appears to differ 

 from neopyrithiamine in the amount of pyrimidine moiety it contains. 

 The formula for neopyrithiamine is given below. 



N=C— NH2-HBr CH3 CH2— CH2— OH 



CHs — C C — CHj 



N— CH Br 



Neopyrithiamine 



Robbins (1941) found low concentrations of pyrithiamine to replace 

 thiamine for Pythiomorpha gonapodyoides (pyrimidine-deficient), while 

 high concentrations inhibited growth. Pyrithiamine did not replace 

 thiamine for Phycomyces blakesleeanus (requires both moieties) or Phyto- 

 phthora cinnamomi (requires intact thiamine). The inhibition of growth 

 of various fungi and bacteria caused by pyrithiamine was overcome by 

 increasing the thiamine content of the medium (Woolley and White, 

 1943). The inhibition index is given in Table 39. The efficiency of 

 pyrithiamine as a thiamine antagonist is related to the specific vitamin 

 requirements of the organisms tested. The inhibition index was low for 

 those species which require intact thiamine, intermediate for those which 

 require either or both moieties, and high for self-sufficient species. 



Table 39. 



The Efficiency of Pyrithiamine as an Inhibitor of Fungus and 

 Bacterial Growth 

 (Woolley and White, Jour. Exptl. Med. 78, 1943.) 



Pyrithiamine was found to inhibit sporulation of Ceratostomella fimbri- 

 ata, Choanephora cucurhitarum, and Chaetomium convolutum (Lilly and 

 Barnett, 1948). This inhibition was overcome by thiamine. Pyrithia- 

 mine was reported to be a more efficient antagonist for diphosphothia- 

 mine than for thiamine when Penicillium digitatum was used as a test 

 organism (Sarett and Cheldelin, 1944). 



