EFFECT OF AMMONIA STARVATION ON HYDROXYLAMINE OXIDOREDUCTASE ACTIVITYOF NITROSOMONAS-EUROPAEA

A technique for detection of the activity of hydroxylamine oxidoreduct ase (HAO) involving denaturing SDS-polyacrylamide gels was developed, The activity of HAO of Nitrosomonas europaea was assayed using this te chnique, which revealed a single active band of 140 kDa, The HAO activ ity of other ammonia-oxidizers was also resistant to SDS, the molecula r weights being identical to that of N. europaea, N. europaea cells st arved of ammonia for up to 72 h retained a considerable amount of HAO, as detected on Western blot analysis, and a significant level of its activity, as found on assaying at the end of the starvation period, On ly after 4 h incubation of starved N. europaea cells with 2.0 mM ammon ia was some increase in the HAO level observed, The results indicate t hat HAO remains highly stable during ammonia starvation of N. europaea .