396 Marine Microbiology 



Engel and Alexander (17, 18) observed a slow disappear- 

 ance of hydroxylamine at the cell-free level with no apparent 

 accumulation of nitrite for periods as high as six hours. They 

 suggested that hydroxylamine activating enzymes may be cataly- 

 zing the reaction with the formation of an "unidentified" inter- 

 mediate whose further conversion does not occur due to the 

 lability of the necessary enzyme. Nicholas and Jones (34) have 

 since reported the conversion of hydroxylamine to nitrite by 

 cell free extracts of Nitrosomonas europca within relatively 

 short periods of twenty minutes if added mammalian cytochrome 

 c or phenazine methosulfate was used as an electron acceptor. 

 They achieved a 40 fold purification of the hydroxylamine enzyme 

 by means of ammonium sulfate and DEAE cellulose fractionation 

 techniques. Although hydioxylamine completely disappeared 

 from the system, nitrite formation ranged from 40 to 73 per cent 

 of the calculated values based on 0--uptake measurements using 

 cell-free extracts and suitable electron acceptors. Their results 

 suggest a possible intermediate, as yet not identified, between 

 hydroxylamine and nitrite. Delwiche et ah, recently reported the 

 results of preliminary experiments with crude cell-free prepara- 

 tions of Nitrosomonas indicating that the formation of high-energy 

 phosphate bonds as adenosine triphosphate (ATP) may accom- 

 pany hydi^oxylamine oxidation ( 15 ) . Anderson ( 9 ) , ruled out the 

 possibility of hyponitrous acid as an intermediate because of the 

 inability of the hydroxylamine activating enzymes to oxidize the 

 added compound. Nitrosomonas extracts, however, in presence 

 of hydroxylamine, decolorized methylene blue anaerobically with 

 an output of gas; but under aerobic conditions methylene blue 

 increased NO-" formation although in quantities which were 

 significantly smaller than the corresponding O- uptake ( 9 ) . In the 

 light of the above observation. Lees (29) sugggesls the following 

 pathway of hydroxylamine oxidation: 



