Physiology 457 



mentary DPN and TPN accelerate oxidation of pyruvate by Plasinodium 

 gallmaceum in the presence of dicarboxylic acids (535). 



Diphosphothiamine enzymes. This phosphoric acid ester of thiamine 

 is the coenzyme of carboxylase which catalyzes the decarboxylation of 

 pyruvic acid and probably certain other a-keto monocarboxylic acids. 

 Supplementary thiamine is necessary for the oxidation of pyruvate by 

 Tetrahymena pyriformis (552), is essential to growth of Chilomonas Para- 

 mecium on pyruvate (73), and accelerates oxidation of pyruvate by Plas- 

 modium gallinaceum (535). The thiamine content of Tetrahymena pyri- 

 formis is at least 60 per cent that of yeast (574), and the vitamin is 

 essential to growth of this and certain other Protozoa (Tijble 8. 3). There- 

 fore, thiaminoprotein enzymes are probably of general importance in 

 protozoan metabolism. 



Flavoprotein ejizymes. In these enzymes the prosthetic groups contain 

 riboflavin, either as riboflavin-phosphate or as flavin dinucleotide (a 

 union of riboflavin-phosphate and adenylic acid). Enzymes of the first 

 type apparently catalyze the oxidation of reduced TPN and oxidation of 

 L-amino acids (L-amino acid dehydrogenase). Enzymes of the second type 

 include xanthine oxidase, D-amino acid dehydrogenase, glycine dehydro- 

 genase, and apparently "diaphorase I" (catalyzing oxidation of reduced 

 DPN). These flavoprotein enzymes, which are not significantly affected 

 by cyanide poisoning, are probably present in Protozoa. Riboflavin occurs 

 in high concentration in Tetrahymena pyriformis (574) and is essential 

 to growth of several ciliates (Table 8. 3), although synthesized by Chilo- 

 monas parajnecium (207). 



Pyridoxine enzymes. Pyridoxal phosphate appears to be the coenzyme 

 for transaminases, tryptophanase, and certain amino-acid decarboxylases. 

 The presence of comparable enzymes in Protozoa may be suspected since 

 pyridoxine is essential to growth of certain ciliates (Table 8. 3) and 

 inhibits the antimalarial action of quinine and atebrine against P. 

 lophurae (519), and also since pyridoxal is synthesized by Chilomonas 

 Paramecium. 



Peroxidase ayid catalase. These are iron-porphyrin-protein enzymes. 

 Catalase probably catalyzes coupled oxidations by means of the hydrogen- 

 peroxide formed in some primary reaction (271), the peroxide being de- 

 composed to water and molecular oxygen. Peroxidase catalyzes the oxida- 

 tion of such substrates as tyrosine, adrenaline, bilirubin, pyrogallol, and 

 various other phenols in the presence of hydrogen peroxide. Peroxidase 

 has been demonstrated in Tetrahymena pyriformis (311) and catalase in 

 certain related ciliates (43, 204), but the activities of neither enzyme in 

 protozoan metabolism have been investigated. 



Glutathione. In the reduced form, this is a tripeptide of glycine, cys- 

 teine, and glutamic acid. Although reduced glutathione has been demon- 



