364 IMMUNO-CATALYSIS 



they play in a complete respiratory system, flavoproteins also function 

 as oxidases (dehydrogenases). This does not involve the participation 

 of dehydrogenases containing coenzyme I or II. d-Amino acid oxidase, 

 l-amino acid oxidase, xanthine oxidase, aldehyde oxidase and fumaric 

 hydrogenase, a mold glucose dehydrogenase, glycine oxidase and cyto- 

 chrome reductase have been shoM^n to be flavoproteins containing either 

 isoalloxazine-d-ribosephosphate, or isoalloxazine-adenine dinucleotide 

 as the coenzymes. 



Permentation: Biological oxidation reactions which cause the revers- 

 ible breakdown of glycogen to lactic acid in muscle in the absence of 

 air, and similar reactions which are brought about by yeast, causing 

 the breakdown of glucose to alcohol are known as fermentation re- 

 actions. Various enzymes and coenzymes which mediate the reactions 

 involved in the fermentation reactions are given below. 



Enzymes Containing Cocarhoxylase: Cocarboxylase is an essential 

 coenzyme of fermentation. In alcoholic fermentation (yeast, plant 

 tissue and bacteria) pyruvic acid is decarboxylated by carboxylase, of 

 which cocarboxylase (thiamine diphosphate) is the coenzyme group. 

 In animal tissue on the other hand, pyruvic acid is reduced to lactic 

 acid. This does not depend on the absence of cocarboxylase in animals 

 but on the specificity of the enzyme, by which the oxidative decom- 

 position is indicated. Cocarboxylase is likewise a component of the 

 enzyme systems known as 'pyruvic dehydrogenase, a-keto-glutaric car- 

 hoxylase, pyruvic ketolase and aldehyde ketolase. 



Heme Containing Enzymes: These catalysts participate in reactions 

 which involve oxygen or hydrogen peroxide as one of the reactants. 

 They all contain heme as the common prosthetic group in combination 

 with specific proteins which regulate the specific activity of each 

 catalyst. There are at least ten known heme containing catalysts. They 

 are: hemoglobin, myoglobin, cytochrome a, h, c, cytochrome oxidase, 

 cytochrome c peroxidase, catalase, peroxidase, and verdo-peroxidase. In 

 most aerobic respirations the cytochrome oxidase system constitutes the 

 terminal oxidizing system. 



A complete aerobic respiratory system comprises the following parts: 

 Dehydrogenase-f-substrate+flavoprotein-j-terminal oxidizing system. 



According to this scheme, the substrate is dehydrogenated (oxidized) 

 by dehydrogenase whereby the coenzyme group (of dehydrogenase) is 

 reduced. The reduced coenzyme is then dehydrogenated by a flavo- 



