Mechanism of the allantoin fermentation.

Allantoin occurs widely in nature, where it arises from the oxidation of uric acid (1, 2). Animals, plants, and bacteria convert allantoin to glyoxylic acid and urea via allantoic acid (14). The aerobic oxidation of allantoin by a species of Pseudomonas has been studied in detail (4), but the pathway of allantoin fermentation is incompletely known. That the aerobic and anaerobic pathways of allantoin degradation possess little similarity was shown by Barker (5), who isolated oxamic acid as a major product of allantoin fermentation by Xtreptococcus alluntoicus. Vogels (6) has recently reported the isolation of two other bacteria capable of fermenting allantoin to oxamate. One organism closely resembles S. alluntoicus. This communication is concerned with the mechanism of the allantoin fermentation. Evidence is presented for a pathway in which allantoic acid, glyoxylurea, and carbamyl oxamate are intermediates in oxamate formation. Evidence is also presented for the rapid production of glyoxylate from allantoin by extracts. The presence of glyoxylate carboligase (7) and tartronic semialdehyde reductase (8) indicates that carbon for biosynthesis in S. allantoicus may proceed through a pathway similar to that described by Kornberg and Gotto (8, 9). Dagley, Trudgill, and Callely (10) have reported recently the occurrence of these reactions in aerobic glycine metabolism by a Pseudomonas. The occurrence of such a pathway would represent a unique method for synthesis of carbon skeletons by an anaerobe. Preliminary reports of some of this work have appeared (11-16).