Nitrogen fixation by cell-free extracts of Klebsiella pneumoniae

Abstract

A cell-free system which permits N fixation by extracts of K. pneumoniae M5al (formerly Aerobacter aerogenes) was developed. It is essentially, the system described for Azotobacter vinelandii, utilizing ATP as a source of energy and dithionite as a source of electrons. The Michaelis constant for fixation was estimated to be 0.12 atmospheres. The extracts possessed an ATP-dependent H evolving system. Hydrogen evolution from these extracts was less under N than under H in the presence of ATP. Nitrogen gas appears to be the inducer of N fixation. In the absence of N2, no induction of nitrogenase occurs. Nitrogenase is absent in cells grown on NH4+-N. There is a lag of about 13 hr. after the introduction of N2 gas into culture which has depleted its supply of NH4+-N before nitrogenase can be detected. Ammonium ion appears to prevent the synthesis of new molecules of nitrogenase without affecting the activity of those already formed.