The enzyme systems responsible for the oxi-be hydrogen donors. Among these were: alanine, dative deamination of amino acids have been valine, leucine, isoleucine. Other amino acids extensively studied in higher organisms, in some were found to reoxidize reduced phenosafranin, facultative anaerobic bacteria such as Proteu benzylviologen and methylviologen in the pres-vuljaris and Proteus moranii, and in some fungience of a suspension of the same organism; that such as Neurospora crassa [cf. general reviews byis, they were shown to be hydrogen acceptors. Krebs (1, 2)]. These enzyme systems are char-Examples of such amino acids were: glycine, acterized by the use of molecular oxygen as a proline, hydroxyproline, ornithine. Stickland final functional hydrogen acceptor. With the then showed that the interaction of a donor and obligate anaerobes, the supposed toxicity of acceptor amino acid in the presence of a bacoxygen for these organisms has somewhat re-terial suspension results in a mutual domination tarded the studies on the oxido-reduction en-as determined by ammonia formation. zymes. Only recently has work on the enzyme As examples of such coupled deaminations we systems, involved in the coupled deanination may cite alanine+ proline and alanine+ discovered by Stickland (3, 4, 5, 6) and Woods glycine; the over-all reactions can be represented (7), been taken up again. as follows: