IV. BIOCHEMICAL SYSTEMS 355 



is as follows : 



CH.NHRCOOH + oxidized enzyme — ^ CH=NRCOOII + reduced enzyme 



CH=NRCOOH + HoO -> CHOCOOH + NH2R 



Reduced enzyme + O2 — > oxidized enzyme + H2O2 



Methylene blue can be reduced when the reaction is carried out anaerobi- 

 cally. 



13. FuMARic Hydrogen ASE 



The only example to date of a flavoprotein enzyme system in which an 

 organic substrate is a hydrogen acceptor was discovered in yeast by Fischer 

 and Eysenbach^^ and Fischer et al.^^ Fumaric hydrogenase from yeast 

 catalyzes the reduction of fumaric acid to succinic acid by the reduced 

 forms of various oxidation-reduction dyes. Fumaric acid seems to be a 

 specific hydrogen acceptor, but to date no naturally occurring hydrogen 

 donor has been found for this reaction. 



The enzyme is present as an impurity in the preparation of Warburg 

 and Christian's old yellow enzym'e, from which it can be separated by 

 cataphoresis in alkaUne solutions. ^^ The prosthetic group is flavin adenine 

 dinucleotide. 



The reduction of fumarate was demonstrated as follows: 



Methylene 

 violet 



COOH 



I 

 Leuco- H— C— COOH CH2 



methylene + || — ^ I "t" 



violet HOOC— C— H CH2 



• I 



COOH 



Fumaric acid Succinic 



acid 



Fumarate can be replaced in this system^^ by maleate, crotyl alcohol, 

 phenylcrotyl alcohol, and geraniol. Hyposulfite can replace the reduced 

 dyes as reductants of the enzyme. 



The turnover number of this reductase is about 2700. 



14. Glucose Oxidase of Molds 



Penicillium notatum produces a flavoprotein which oxidizes glucose to 

 gluconic acid in the presence of oxygen. Because hydrogen peroxide accu- 

 mulates as a result of its action, it was prematurely classified as an anti- 



" F. G. Fischer and H. Eysenbach, Ann. 530, 99 (1937). 



'' F. G. Fischer, A. Roedig, and K. Rauch, Nalurwissenschaften 27, 197 (1939). 



