400 Marine Microbiology 



ability of ferric or ferrous ions to restore the completely inactiva- 

 ted nitrite oxidase resulting from dial) sis of the enzyme against 

 cyanide solution. No other metal could either replace iron or 

 stimulate nitiite oxidation by the purified Nitrobacter particles 

 (4). Zavarin (39) had previously found a stimulation of growth 

 by iron, molybdenum or tungstate and implicated their role in the 

 nitrification process. He postulated a direct participation of mag- 

 nesium and flavins in nitrite oxidation, and reported that 10~^ 

 M iodoacetic acid or sodium tungstate failed to inhibit nitrite 

 oxidation by intact cells; nor was the process apparently affected 

 by specific SH group inhibitors. In the studies of Alecm and 

 Nason (4), it has thus far not been possible to observe a flavin 

 component spectrophotometrically or to show an effect of added 

 FAD, FMN or riboflavin on the nitrite oxidase system. In addi- 

 tion, nitrite oxidase activity was completely suppressed by 10"^ 

 parachlormercuribenzoate and fully restored by the addition 

 of 10^ M cysteine or glutathione. The nitrite oxidase system has 

 also been found to be highly sensitive to cynide, azide and other 

 metal binding agents as well as to relatively high concentrations 

 of certain respiratory chain inhibitors, e.g., antimycin A and 

 heptyl-4 hydroxyquinoline-N oxide (5, * * ) . 

 . . . Nitrobacter like many other aerobic micro-organisms pos- 

 sesses cytocliromes which have been implicated to be directly con- 

 cerned with nitrite oxidation. Lees and Simpson (28) observed 

 that Nitrobacter cells treated with nitrite in presence of chlorate 

 showed a gradual fading of the cytoclirome bands, especially at 

 551 m,", and a corresponding decrease in 0--uptake. Cyanate in- 

 hibited nitrite oxidation and apparently accounted for the failure 

 of the 551 band to appear upon addition of nitrite or ditliionite. 

 These observations led Lees and Simpson to suggest that the 

 cytochrome with absorption maximum at 551 m/x is intimately 

 concerned with nitrite oxidation. Zavarzin (39) confirmed the 

 results of Lees and Simpson and also implicated flavins in nitrite 

 oxidation. 



Aleem and Nason (4) using a split-beam spectrophotometer* 



* We are indebted to Drs. B. Chance and R. Estabrook for some of these measure- 

 ments. 

 ** unpublished data. 



